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Electrochemical transformation of oxalic acid and nitrate into glycine is an appealing way for valuable chemical synthesis and waste nitrate treatment. Currently, strategies to electrosynthesis of amino acid through catalyst design have been successfully developed, but it is still of huge challenge to realize industrial grade electrocatalytic synthesis of amino acid. Here, we develope an innovative electrochemical method to synthesize glycine from harnessing nitrate (NO 3 -) and oxalic acid in an aqueous electrolyte with a porous PbSnBi alloy catalyst. By means of construction the multiple catalytic sites and regulation electrode surface microenvironment, this strategy produces glycine with high Faraday efficiencies of 57.2 %, high yield rates of 1.125 mmol h−1 cm−2 cat , and average current density up to 1 A cm−2 at −1.5 V vs. SCE potential after 2 h electrolysis. The recycled electrolysis experiment confirms its good stability and practical potential. [Display omitted] • The efficient glycine electrosynthesis from harnessing nitrate and oxalic acid is realized over a porous PbSnBi alloy catalyst. • This strategy produces glycine with high faradaic efficiencies of 57.2 %, high yield rates of 1.125 mmol h−1 cm−2 cat. • The construction of polymetallic sites and the addition of ILs are facilitate the electrosynthesis of glycine. [ABSTRACT FROM AUTHOR]

The sluggish Me (n+m)+ / Me n+ cycle of metal based catalysts set an obstacle for catalytic ozonation, which not only restrained O 3 activation efficiency but also damaged their poor stability. Herein, series of atomic metal-doped g-C 3 N 4 with Me-N-C electron transport channels and the photocatalytic ozonation process (PCO) were designed to refresh metal active sites by photo-electron (e cb - ) and overcome the basic need of sacrificing catalysts' inherent electron to activate O 3 into •OH. Experimental and DFT results demonstrated that, oxalic acid degradation in PCO was metal-dependent and followed the trends: Fe-CN (98.5%, 0.228 min−1)>Mn-CN (98.9%, 0.154 min−1)>Co-CN (93.7%, 0.097 min−1). Two distinct •OH generation pathways were proposed. Fe-N-C and Co-N-C were capable of utilizing e cb - to boost metal r e dox cycle and they activated O 3 by e cb - . But Mn-N-C failed to realize such redox cycle and activated O 3 with Mn center sacrificing its inherent electron. This study was useful for designing catalysts for PCO. [Display omitted] • Atomic Fe, Mn and Co with metal-N-C unit enhanced activity of g-C 3 N 4 in PCO of OA. • e cb - could be stored by atomic Fe and Co-CN and used to activate O 3 into •OH. • Mn-CN failed to store e cb - and activated O 3 by sacrificing its inherent electron. • Two O 3 activation pathways based on metal-N-C electron channel were proposed. [ABSTRACT FROM AUTHOR]

An efficient, eco-friendly and cost-effective strategy for the recovery of precious metals from spent lithium-ion batteries (LIBs) is of great significance for the sustainable natural resource utilization and environmental protection. Herein, a low-temperature solid-to-solid reaction combined water leaching technology is proposed for the preferential extraction of Li from spent LiCoO 2 batteries. In the solid-to-solid reaction, crystal water released from the oxalic acid dihydrate acts as a lubricant and initiates the reduction reaction to convert the spent LiCoO 2 into water-soluble Li salts (LiHC 2 O 4 or Li 2 C 2 O 4) and water-insoluble CoC 2 O 4. After water leaching, the collected Li-rich solution and the Co-rich residue are separately transformed into Li 2 CO 3 and Co 3 O 4. Additionally, a defect-enriched Co 3 O 4 is prepared by water quenching process, exhibiting excellent performances towards oxygen evolution reaction. This work not only achieves a facile, low-cost and energy-saving strategy for recycling spent LIBs, but also proposes a vacancy-defected engineering route for electrocatalyst design in energy-related applications. [Display omitted] • A low temperature solid-to-solid reaction combined with water leaching is proposed for LIBs recycling. • The high pressure steam in an enclosed space facilitates the Li separation efficiency. • Oxygen and cobalt vacancy are introduced into Co 3 O 4 by a water quenching process. • Defective Co 3 O 4 exhibits excellent performance towards OER. [ABSTRACT FROM AUTHOR]

Doping other metals such as Mn, Ni, In, et al. is known as an effective strategy to improve the environmental catalytic performance of Co 3 O 4. In our works, Mn ions were successfully incorporated into the lattice of Co 3 O 4 via the oxalic acid synchronous complexation method. The Mn ions preferentially occupy octahedrally coordinated Co3+ sites and constructing the Mn-O-Co structure. In addition, theoretical calculation further verified that the enhanced catalytic performance of Co5Mn1 originated from highly reactive lattice oxygen coordinated with both Mn and Co ions. Significantly, Mn ions transfer more electrons to lattice oxygen. This oxygen sites have the lower oxygen vacancy formation energy (E Ov = 1.94 eV), allowing the lattice oxygen to participate in the reaction following the MvK mechanism in the high temperature range. Collectively, this work is helpful to understand the mechanism of effect of Mn ion doping on the physical and chemical properties of Co-based catalysts. [Display omitted] ● The doped Mn ions occupy the octahedral sites with Mn3+ or Mn4+. ● Induced oxygen vacancies improve the catalytic activity by facilitating the conversion of key intermediate species. ● Mn ions modulate the local charge of the Mn-O-Co structure, and the orbital hybridization enhances the electron transfer. [ABSTRACT FROM AUTHOR]

Valorization of waste polyolefins by a sequential combination of thermal pyrolysis and catalytic hydroconversion over a bifunctional metal/acid catalyst (e.g. zeolite) is an efficient route to produce transportation fuels. However, the zeolite strong acidity typically causes extensive cracking and loss of liquid fuels. In this work, mild dealumination with oxalic acid of a hierarchical Beta zeolite was used to achieve Ni 7%/h-Beta catalysts with Si/Al ratios within the 25 – 130 range. These catalysts were tested in the hydroconversion of a model mixture of LDPE thermal pyrolysis product (1-dodecene/n-dodecane, 50/50 w/w). The highest share of liquid fuels (∼ 90%) was achieved over 7% Ni/h-Beta (SiAl = 130). Besides, due to its high accessibility and tailored acidity, the product contained a meaningful amount of isoparaffins (12%) and a negligible content of olefins (< 3.5%). Thus, this catalyst holds promise for plastic waste hydroconversion towards transportation fuels. [Display omitted] • Hierarchical Beta with tailored acidity achieved by oxalic acid dealumination. • Brønsted acidity decreased after dealumination but did not completely disappear. • Dealuminated Ni/h-Beta: promising catalyst for plastics cracking oil hydroconversion. • Cracking/hydroisomerization balance adjusted by the zeolite Al content. • Highly dealuminated Beta samples keeps significant hydroisomerization activity. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel J-J type Zn m In 2 S m+3 @In 2 S 3 heterojunction was designed based on conductive anisotropy. • The J-J type heterojunction was fabricated with the assistance of oxalic acid. • The heterojunction improves the carrier separation efficiency and extends light response range. • The heterojunction exhibits significantly enhanced photocatalytic H 2 evolution activity. Abstract It remains a great challenge to design and prepare highly efficient semiconductor-based photocatalysts for water splitting. To achieve this goal, the design of oriented heterojunctions for efficient carrier transport and separation is a new strategy based on their conductive anisotropy. Herein, a novel oriented J-J type Zn m In 2 S m+3 @In 2 S 3 heterojunction photocatalyst with hierarchical structures is fabricated with the assistance of oxalic acid. The hierarchical structures consist of 'flower-like' hollow Zn m In 2 S m+3 microspheres with epitaxially grown quantum confined In 2 S 3 along the petal rims (J-J type heterojunction). This heterojunction improves the transport and separation of the photoexcited carriers, and extends the visible-light response range. Thus, the heterojunction photocatalyst exhibits significantly enhanced photocatalytic activity with a hydrogen evolution rate of 330 μmol h−1, which is about 4 times higher than that of single ZnIn 2 S 4. The findings provide new insights to construct efficient oriented heterojunctions for anisotropic semiconductors. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • rGO addition efficiently boosts charge transfer and therefore photocurrent values. • Lower charge transfer resistance found in TiO 2 -rGO led to higher O 2 reduction current. • Low differences in O 2 − and HO were detected in the O 2 saturated suspensions. • The role of rGO as an electron acceptor is less significant in O 2 atmosphere. Abstract Different studies to unravel the nature of the activity of TiO 2 photocatalysts modified with rGO were carried out. The band edge potentials and the band gap energy of the nanocomposites were determined by performing electrochemical impedance and UV–vis diffuse reflectance measurements, respectively. However, no changes were observed when TiO 2 is modified with rGO. Nevertheless, the presence of rGO in the hybrid composite led to a low charge transfer resistance across the electrode-electrolyte interface, observing even a tenfold increase in the photocurrent values in methanol photo-oxidation for P25-rGO 1%. Moreover, a higher oxygen reduction current was found when increasing the rGO concentration that could lead to a higher ROS formation. In order to analyze the beneficial properties of the hybrid materials, the influence of rGO doping ratio on oxalic acid photocatalytic degradation and on oxalic acid adsorption onto the nanocomposites surface was studied, both of them under UV-A light irradiation. In addition, the photoactivity of the conduction band electrons and the valence band holes was investigated by performing EPR and transient absorption spectroscopy measurements under UV-A illumination in O 2 or N 2 atmospheres. It was demonstrated that rGO behaved as an electron acceptor. Finally, TAS results under O 2 and N 2 atmospheres proved that the role played by rGO was not as crucial in excess of dissolved O 2 as in N 2 atmosphere. These findings agree with the observed photocatalytic activity and EPR measurements. Nevertheless, generation of HO in N 2 saturated suspensions was highly increased with the addition of rGO. [ABSTRACT FROM AUTHOR]

Cu 2 O/TiO 2 (1–10 wt% Cu 2 O) and 2.5% Cu 2 O/TiO 2 -AC (2.5–20 wt% AC) photocatalyst composites were synthesised by an ethanol reduction method. The materials were characterised by a number of techniques which confirmed the presence of Cu 2 O in contact with the TiO 2 . Pure TiO 2 alone was not active for the simultaneous photocatalytic removal of nitrate and oxalic acid under conditions employed, however, photocatalytic activity was observed for TiO 2 and TiO 2 /AC in the presence of Cu 2 O. This may have resulted from suppression of charge recombination via creation of a p - n heterojunction between Cu 2 O and TiO 2 . Within the series, 2.5% Cu 2 O/TiO 2 exhibited the best photocatalytic performance with 57.6 and 99.8% removal of nitrate and oxalic acid, respectively, with selectivities of 45.7, 12.4 and 41.9% to NH 4 + , NO 2 − and N 2 , respectively after 3 h. For the carbon containing photocatalysts, 2.5% Cu 2 O/TiO 2 -2·5AC displayed the highest activity with 42.5 and 96.6% removal of nitrate and oxalic acid, respectively, with 32.7, 11.6 and 55.7% selectivities to NH 4 + , NO 2 − and N 2 , respectively. The highest AC loading tested resulted in selectivity to NH 4 + of 21.6 with no NO 2 − detected, together with an improved N 2 selectivity (78.4%) albeit at lower (12.7%) nitrate conversion. Data suggests that Cu 2 O/TiO 2 can be used in the photocatalytic reduction of nitrate and improved selectivity towards N 2 can be attained by influencing factors which control the relative rate of oxalic acid consumption. [ABSTRACT FROM AUTHOR]

Phase-pure monoclinic VO 2 (M) was successfully synthesized by hydrothermal reduction method using oxalic acid as a reductant and solvent-thermal reduction method using methanol as a reductant. Oxidative desulfurization (ODS) activities were investigated and the results revealed that intrinsic ODS activity increased with increasing cell volume for different synthesized VO 2 (M) catalysts. DSC measurement gives the evidence that phase transition temperature of monoclinic VO 2 (M) to rutile VO 2 (R) decreased with increasing cell volume for different VO 2 (M) catalysts. Variable-temperature in-situ Raman spectrum also confirmed that phase transition from VO 2 (M) to VO 2 (R) occurred. Mechanism of ODS reaction on VO 2 (M) catalyst was investigated precisely involving temperatures which phase transition occurred. Below the phase-transition temperature VO 2 (M) showed higher ODS reaction activation energy, while above the phase-transition temperature VO 2 (R) exhibited lower ODS activation energy. This result may be explained by the fact that V O bond length for VO 2 (R) (1.93 Å) fits more for the five-member ring formed with the oxidant tert -butyl hydroperoxide (TBHP) during ODS reaction compared with V-O bond length for VO 2 (M) (about 2.03 or 1.86 Å). [ABSTRACT FROM AUTHOR]

A novel metal-free oxygen doped porous graphitic carbon nitride (OA-g-C 3 N 4 ) was synthesized by condensation of oxalic acid and urea. The 40% OA-g-C 3 N 4 catalyst can degrade bisphenol A (15 mg L −1 ) in 240 min with a mineralization rate as high as 56%. The markedly higher visible-light-driven oxidation activity of OA-g-C 3 N 4 is attributed to the porous morphology and unique electrical structure. The porous structure of OA-g-C 3 N 4 provides more active sites for adsorption and degradation of pollutants. Moreover, oxygen atoms in the tri-s-triazine units help to extend sufficient light absorption range up to 700 nm, improve the separation of charge-carriers and alter the position of valence band (VB) and conduction band (CB). The VB edge shifts from 1.95 eV to 2.46 eV due to the incorporation of O atoms, which leads to the change of active species in the photocatalytic reaction. Trapping experiment shows that superoxide radicals play the major role in the photocatalytic degradation of BPA on g-C 3 N 4 , while hydroxyl radical is the dominant active species in the photocatalytic degradation process over 40% OA-g-C 3 N 4 . This study presents a simple, economical and environment-friendly method to synthesized oxygen doped porous graphitic carbon nitride. [ABSTRACT FROM AUTHOR]

Nanostructured niobium oxides were synthesized by hydrothermal treatment using an amorphous Nb 2 O 5 as precursor. The modification by hydrothermal treatment in the presence of oxalic acid or hydrogen peroxide resulted in versatile catalysts with many different properties verified by several characterization techniques. XRD analysis demonstrated the crystallinity increase. Significant morphological changes were observed by TEM, being possible to observe the presence of nanorods for the material treated with oxalic acid and nanospheres for the material treated in the presence of H 2 O 2 . Modifications in the porous structure were also observed, as well as the increase in BET specific area. This significant difference compared to precursor resulted in catalysts with higher performance than Nb 2 O 5 in decomposition of methylene blue dye (MB) by heterogeneous fenton-like reactions and photocatalysis under UV light irradiation. [ABSTRACT FROM AUTHOR]

Co-ZFO@Mn-CN with 1O 2 and O 2 •− as main reactive oxygen species was synthesized for catalytic ozonation, which could efficiently degrade organic pollutants. EPR and XPS analysis indicated that lattice doping of Co induced formation of abundant of OVs, which could provide localized electrons for O 3 activation with the generation of HO 2 •/O 2 •−. 1O 2 and H 2 O 2 were produced by the recombination of HO 2 •/O 2 •−. DFT calculation demonstrated that H 2 O 2 was deprotonated to generate HOO−, which preferred to form HOO-Mn-N X bonds with Co-ZFO@Mn-CN. Under the attack of O 3 , HOO-Mn-N X bonds were broken with the generation of HO 2 • and HO 3 •/O 3 •−, not only accelerating 1O 2 production for organics degradation but also avoiding Mn(Ⅱ) sites oxidation. Combining advantages of OVs and HOO-Mn-N X , Co-ZFO@Mn-CN achieved 70–100% mineralization for different organic pollutants. Thus, this work provided a simple and efficient way for enhancing the utilization of O 3 by the synergistic effect of OVs and HOO-Mn-N X bonds, also improving ROS transformation. [Display omitted] • Co-ZFO@Mn-CN is constructed with 1O 2 and O 2 •− as main ROS for catalytic ozonation. • Doping of Co induce formation of OVs for O 3 activation with production of HO 2 •/O 2 •−. • HO 2 •/O 2 •− recombine to produce 1O 2 /H 2 O 2 , and HOO- bind catalyst to form HOO-Mn-N X. • O 3 help to break HOO-Mn-N X with generation of HO 2 • and HO 3 •/O 3 •− for 1O 2 production. • Synergistic effect of oxygen vacancies and HOO-Mn-N X bond accelerate ROS production. [ABSTRACT FROM AUTHOR]

Oxalic acid (OA), together with its ligand, appears in diverse biotic and abiotic processes in nature. However, the applications of the photochemical property of OA and its complexes in environmental purification are scarce. Herein, we reported a Fe single-atom catalyst with Fe-N 4 configuration supported on g-C 3 N 4 (Fe-CN) to activate OA for ultrahigh-efficiency removal of Cr(VI) under visible light irradiation through dual pathways: the photo-dissociation of [FeⅢ(C 2 O 4)]+ and the reaction between OA and photogenerated holes, achieving the generation of •CO 2 -. The introduction of Fe-N 4 favors the formation of configuration [FeⅢ(C 2 O 4)]+ and fabricates the electron transfer channel from catalyst to OA, further decreases the energy barriers of •CO 2 - generation, and thereafter efficiently facilitates the C-C cleavage for the generate of •CO 2 -. Meanwhile, the strong coordination interaction over Fe single atoms and N atoms could enhance the separation efficiency of photo-carriers and further promote the reduction activity. Under optimal conditions, Fe-CN showed a 5.1-fold increasement in photocatalytic kinetics contrast to pristine CN. The Fe-CN catalyst attached on fibrous membrane for treatment of flowing Cr(VI) wastewater exhibits 90% reduction efficiency over 10 h, which is expected to facilitate the practical application of the catalyst. The mechanism of OA activation with dual-pathway was unveiled by in-situ Fourier transform infrared spectra and theoretical calculations. This work provides an important guidance for the application of OA and its complexes to achieve the attenuation of toxic and harmful heavy metal in water restoration. [Display omitted] • The Fe single-atom catalyst was fabricated to OA activation for Cr(VI) detoxification. • The introduction of Fe-N 4 favors OA activation under visible irradiation through dual pathways. • The photo-dissociation of Fe-OA complex was unveiled based on the in-situ DRIFT and DFT calculations. • The Fe-N 4 active sites enhanced separation and migration of photocarriers, further accelerating the generation of •CO 2 -. • The combination of membrane technology with catalysis exhibits great stability, activity and retention effect. [ABSTRACT FROM AUTHOR]

The performance of novel N-doped carbon materials prepared by an easy ball milling method was evaluated in two distinct advanced oxidation processes (AOPs): catalytic wet air oxidation (CWAO) and catalytic ozonation (COZ), using oxalic acid as model pollutant. The ball milling method allows the incorporation of large amounts of N-groups onto the surface of carbon nanotubes, namely pyridine-like N atoms (N-6), pyrrole-like N atoms (N-5) and quaternary nitrogen (N-Q), resulting in highly active catalysts for the oxidation of oxalic acid by both AOPs. The material prepared by ball milling with melamine without solvent is the most promising sample, combining an easy preparation with high amount of N-functionalities. Under the operation conditions used, oxalic acid was completely mineralized in 5 min by CWAO and in 4 h by COZ. The novel metal-free catalyst developed by this easy ball milling method demonstrated to be effective, confirming that this solvent-free methodology is quite adequate for the preparation of N-doped carbon materials with enhanced properties for the mineralization of organic pollutants by the studied processes. [ABSTRACT FROM AUTHOR]

Degradation of aqueous solutions of oxalic acid (OXA) and oxamic acid (OMA), the final oxidation products of several organic compounds, has been investigated by photocatalytic ozonation. The combined method was carried out comparing P25 to synthesized sol–gel TiO 2 , and composites of TiO 2 and multi-walled carbon nanotubes (MWCNTs) obtained either by the sol–gel method or by the hydration–dehydration technique. Photo-ozonation in the presence of P25 resulted in total conversion of OXA after 15 min. Concerning OMA, P25 and composites containing 80 and 90% wt of P25 led to complete degradation more rapidly. The reaction rate constants, k app , were 15 × 10 −2 min −1 for P25, 8.8 × 10 −2 min −1 and 8.2 × 10 −2 min −1 for the composite with 80 and 90% wt of P25, respectively. OMA removal by photocatalytic ozonation is here reported for the first time and a remarkable conversion is obtained with complete degradation achieved in a short period of time in the presence of TiO 2 , P25 and composites with 80 and 90%wt of P25 and MWCNTs and with 80%wt of P25 and oxidized MWCNTs. By performing single photocatalysis or single ozonation for selected materials, a synergetic effect of the combined method was identified. [ABSTRACT FROM AUTHOR]

Heat/persulfate (PS)-based chemical oxidation for soil and groundwater remediation is limited in its ability to degrade highly chlorinated compounds (HCCs) due to their insensitivities to electrophilic radicals (e.g. SO 4 • - and O • H). Herein, we developed a universal system for reductive radicals formation with nucleophilic character through hydrogen atom transfer between low-molecular-weight organic acids (LMWOAs) and electrophilic radicals. Specifically, we found that oxalic acid could regulate heat/PS system to generate carbon dioxide radical anion (CO 2 • -) which initiated nucleophilic reduction of dichlorodiphenyltrichloroethane (DDT), followed by SO 4 • - / O • H -initiating electrophilic oxidization of dechlorination intermediates. The CO 2 • - was oxygen-dependent, resulting in higher DDT degradation performance in anaerobic environment, and corresponding degradation pathways were elucidated by theory calculations. Most importantly, compared to heat/PS system, appropriately distributing the amount of CO 2 • - and SO 4 • - / O • H by regulating additive concentration of oxalic acid significantly increased degradation efficiency (32.34%), degradation rate (174.20%), and mineralization efficiency (29.57%) on DDT, revealing great potentials of proposed system. [Display omitted] • Low-molecular-weight organic acids (LMWOAs)-regulating heat/PS system is developed. • Carbon dioxide radical anion formed in heat/PS/OA system by hydrogen atom transfer. • The role of oxalic acid with different concentration in heat/PS/OA system is studied. • Synergistic mechanism of reductive/oxidative radicals is investigated thoroughly. • Degradation pathways of DDT and reaction mechanism of heat/PS/OA system are proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] SiO2-crystalline TiO2 photoactive materials have been successfully synthesized. [•] These materials meet requirements as self-cleaning and hydrophobic coatings for stone. [•] In this synthesis, oxalic acid produces anatase crystals at ambient conditions. [•] Oxalic acid promotes the simultaneous sol–gel transition for Ti and Si alkoxides. [•] Oxalic acid also increases the photoactivity by acting as a hole-scavenger. [Copyright &y& Elsevier]

Highlights: [•] CNTs functionalized with O- and S-containing surface groups. [•] Liquid-phase degradation of oxalic acid and phenol by CWAO using CNTs as catalyst. [•] Carboxylic acid groups (higher acidity) decrease the catalytic activity of CNTs. [•] S-containing surface groups significantly increase the catalytic activity of CNTs. [Copyright &y& Elsevier]

Highlights: [•] Nitration treatment enhanced the activity of activated carbon in catalytic ozonation. [•] The amination modification enhanced the activity of activated carbon in catalytic ozonation. [•] Acid oxygenated groups play a positive role in catalytic ozonation of oxalic acid. [•] This provides a new choice to promote the activity of activated carbon in catalytic ozonation. [Copyright &y& Elsevier]

At present, it is still a challenge to develop ozone decomposition catalysts with high efficiency and high humidity resistance. Herein, a series of spinel (Mn,Co) 3 O 4 catalysts are synthesized by coprecipitation method. Compared with the Mn 3 O 4 and Co 3 O 4 analogues, the obtained (Mn,Co) 3 O 4 has Co Co III II × acceptor-defect and Mn Mn II III × donor-defect, which could contribute to the electron transfer between catalyst and ozone, accelerating ozone decomposition. Importantly, the in-situ Raman spectra of Mn 3 O 4 shows the accumulation of peroxide species (O 2 2-) inferring that the decomposition of O 2 2- is the rate-determining step. On the other side, the reaction of the atomic oxygen with ozone would be rate-determining for Co 3 O 4 , as revealed by the low efficiency but no O 2 2- signal. However, the synergy of Mn and Co in (Mn,Co) 3 O 4 accelerates both the rate-determining steps obtaining high efficiency, which provides a new idea to develop catalysts in ozone elimination. [Display omitted] • Spinel (Mn,Co) 3 O 4 catalysts were synthesized by oxalic acid coprecipitation. • (Mn,Co) 3 O 4 catalysts show high ozone decomposition efficiency in harsh conditions. • The synergy of Mn and Co accelerates the rate-determining step of ozone decomposition. [ABSTRACT FROM AUTHOR]

Highlights: [•] La containing perovskites are tested as ozonation catalysts. [•] Perovskites of the type LaBO3 are highly active in oxalic acid ozonation. [•] Presence of lattice vacancies and tuning of oxidation ability by the B cation play a key role. [•] The mechanism involves both surface and liquid bulk reactions. [•] LaCoO3 promoted ozonation of the reactive dye tested allows complete mineralization. [Copyright &y& Elsevier]

Abstract: Ozone initiated oxidation of tetrachloro-o-benzoquinone (3,4,5,6-Tetrachlorocyclohexa-3,5-diene-1,2-dione, TCCD) in aqueous system catalyzed by different loadings of cesium oxide supported on metal oxides namely; Al2O3, SiO2 and TiO2 was investigated. Catalyst materials were characterized using different surface techniques including Raman, FT-IR, BET, SEM, TEM, ICP, TPD and XRD. XRD showed that cesium is in three different phases on the surface of the catalysts; and SEM and SEM-EDX indicated that cesium is well dispersed on the surface of the supports. Catalyst testing was done employing varying ozone molar ratios from 1 to 3 in the oxygen stream in a semi-batch reactor. 2,3-Dichloro-4,5-dioxohex-2-enedioic acid (DCA) was an intermediate and 2,3-dioxosuccinic acid (DSA) and oxalic acid (OA) were the main oxidation by-products. The oxidation products were characterized and confirmed by IR, 1H NMR and Mass spectral data. The product distribution was dependent on the acidity of the supports. Among all the catalysts while 5% Cs/TiO2 showed good activity, 1% Cs/SiO2 showed relatively poor catalytic activity. [Copyright &y& Elsevier]

Abstract: Carbon xerogels prepared at different pH and ceria–carbon xerogel materials with different compositions and synthesized by different procedures were evaluated as catalysts in the ozonation of oxalic acid and the textile dye CI Reactive Blue 5. The prepared samples were characterized by N2 adsorption at −196°C, X-ray diffraction and scanning electronic microscopy. All the catalysts containing both cerium oxide and carbon xerogel removed all oxalic acid in solution after 1h of reaction. Cerium oxide supported on carbon xerogel and carbon xerogel containing 1% of cerium oxide prepared by one-pot synthesis were the most active catalysts for the ozonation of the dye solution. Considering the catalytic activity and the steps involved in the preparation of materials, the carbon xerogel containing 1% of cerium oxide prepared by one-pot synthesis is the most promising catalyst. [Copyright &y& Elsevier]

Abstract: Magnetic cobalt-doped Fe3O4 (FeCo) was prepared using a co-precipitation method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The catalyst showed high, stable catalytic activity for the degradation and mineralization of toxic persistent organic pollutants, as demonstrated with the herbicides 2,4-dichlorophenoxyacetic acid, 2,4-dichlorophenol, and 2,4,6-trichlorophenol and pharmaceutical phenazone in aqueous solution with ozone. FeCo was very effective at the mineralization of refractory oxalic acid produced in the degradation of organic compounds. The ozone was adsorbed on the surface of FeCo competing with water molecules in the aqueous phase, and converted into hydroxyl radical, meanwhile the catalyst surface underwent oxidation and reduction as demonstrated by in situ ATR-FTIR, CV and other experimental data obtained. Furthermore, the characterization studies indicated that the introduction of Co increased the rate of FeCo oxidation and reduction during the decomposition of ozone, enhancing the activity and stability of Fe3O4. [Copyright &y& Elsevier]

Abstract: Several catalysts of cerium oxide highly dispersed on activated carbon were prepared varying the cerium precursor, the solvent and the chemical surface properties of the support, and characterized by several techniques. Afterwards, these materials were investigated as ozonation catalysts for the mineralization of two organic compounds (oxalic acid and aniline). The ozonation results were compared with those obtained in the absence of catalyst and in the presence of the parent activated carbons used for the preparation of these materials. The prepared catalysts have better performances than the parent activated carbons, denoting a clear synergic effect between activated carbon and cerium oxide. The efficiency of the catalysts is mainly affected by the amount of Ce3+ species on the surface. However, in the ozonation of oxalic acid, the specific surface area and metal oxide particle diameter also played an important role. The use of activated carbon as support favors the removal of both organic compounds studied. Highly dispersed cerium oxide on activated carbon shows better catalytic performance than a composite with the same composition. [Copyright &y& Elsevier]

Abstract: Different chemical and thermal treatments (nitric acid at boiling temperature, liquid-phase urea treatment at 200°C, and gas-phase thermal treatment with nitrogen at 600°C) were applied to multiwalled carbon nanotubes (MWCNTs) in order to produce materials with different textural and chemical properties. Nitrogen adsorption isotherms, temperature programmed desorption, pHpzc (point of zero charge), elemental analysis and X-ray photoelectron spectroscopy were used to characterize these materials. The chemical and thermal treatments have influence on the materials pHpzc, which decreases upon nitric acid treatment and increases with urea or gas-phase thermal treatments. The original and modified MWCNTs, without any impregnated metal, were investigated as catalysts in the catalytic wet air oxidation (CWAO) process, using oxalic acid as model compound at 140°C and 40bar of total pressure. Oxalic acid is very stable under non-catalytic conditions but can be totally degraded in less than 30min in the presence of MWCNTs. The rate of oxidation of oxalic acid depends on the chemical properties of MWCNTs, the apparent initial first-order rate constants being lower for the MWCNTs with a marked acid character. The textural properties of MWCNTs are stable in cyclic CWAO experiments, but a decrease of their basic character leads to the reduction of their catalytic activity, even if this activity is still high with reused catalysts (nearly total oxalic acid degradation in 45min and complete mineralization in 120min). Therefore, MWCNTs without any impregnated metal, especially those of more basic character, are very active catalysts for CWAO, their activity strongly depending on the stability of their surface chemistry. [Copyright &y& Elsevier]

Abstract: This study aims in analyzing, at laboratory scale, the mechanisms and performances of 2,4,6-Trinitrotoluene (TNT) removal from contaminated water using electro-Fenton process. This treatment belongs to the group of advanced oxidation processes (AOPs), regarded as the most effective approach to decontaminate wastewater from persistent and toxic organic pollutants. In this study, the TNT degradation was investigated through high resolution LC–ESI–MS/MS to tentatively identify the aromatic by-products. The proposed degradation scheme shows a complex alternation of oxidation and reduction mechanisms, evidencing the importance of the electrochemical reduction in the whole process. Furthermore, oxidative opening of the highly reduced/oxidized TNT aromatic ring occurred rapidly during the treatment, leading to the transient accumulation of short chain carboxylic acids such as malonic, glyoxylic, oxalic and formic acids. Mineralization occurred but was delayed in front of TNT and carboxylic acids, showing the persistence of some recalcitrant by-products. [Copyright &y& Elsevier]

Abstract: Cerium oxides prepared by the precipitation method and hydrothermal synthesis, with distinct morphologies and particle size, were tested as catalysts in the ozonation of selected organic compounds. Oxalic acid, aniline and a reactive dye were used as representative of organic pollutants. In the case of oxalic acid, an increase in the catalytic activity with the increase of the percentage of Ce(III) on the surface was observed. Both single and catalytic ozonation allowed the total removal of aniline after 30min of reaction; the cerium oxide prepared by the precipitation method was the best catalyst for promoting the mineralization of aniline solutions. TOC removals close to 100% were obtained in all cases when cerium oxides were used as catalysts in the ozonation of the reactive dye tested. [Copyright &y& Elsevier]

Abstract: Cerium oxide–carbon composites were prepared and tested as ozonation catalysts for the removal of two selected carboxylic acids, oxalic and oxamic, and one textile dye (C.I. Reactive Blue 5). The results were compared with those obtained in non-catalytic ozonation and ozonation catalysed by cerium oxide and carbon materials (activated carbon, carbon xerogel). With the exception of cerium oxide, a total degradation of oxalic acid was obtained in approximately 90min for all prepared catalysts and the catalytic activity increases with the amount of carbon present in the composites. Despite of oxamic acid be more refractory to ozonation than oxalic acid, 75% of oxamic acid removal was achieved after 10h of reaction in the presence of the ceria-activated carbon composite with 90% of carbon material. In the mineralization of the textile dye, the catalytic activity of the composites increases with the amount of activated carbon introduced. [Copyright &y& Elsevier]

Abstract: The effects of pH on the performance of different photocatalytic oxidizing systems involving iron oxides, oxalic acid, hydrogen peroxide and titanium dioxide for the removal of bisphenol A (BPA) and its degradation phenolic intermediates, have been studied. For that purpose two photoreactors have been used: one irradiated with black light lamps and the other with solar radiation. Effects related to iron dissolution, generation/photoreduction of ferrioxalate and accumulated UV-A energy in the photoreactors are discussed in terms of BPA and total polyphenol (TP) degradations, TOC elimination (i.e., mineralization), accumulation of iron in solution and hydrogen peroxide disappearance rate. Solar radiation was found to be more efficient than the black light lamps used due to the higher flux of UV-A radiation supplied. When results were expressed as a function of the accumulated UV-A energy, however, no significant differences were observed on organic degradation rates when using one or another radiation source with the exception of the systems where hydroxyl radical formation goes through, at least in some extent, iron oxides dissolution in the presence of oxalic acid. For these cases, in addition to the accumulated UV-A energy, contact time between oxalic acid and iron oxides played a key role in the process. [Copyright &y& Elsevier]

Abstract: The influences of treatment conditions, gas atmosphere (N2 and H2) and temperature (450°C and 950°C), on the surface properties and catalytic performance of carbon nanotube (CNT) were investigated for the degradation of oxalic acid in aqueous solution by the process of catalytic ozonation. No obvious change on the textural properties of CNT is found after heat treatment, while the results of Boehm titration clearly indicate the reduction of acidic groups and the increase of basic groups on CNT surface after heat treatment under different conditions, and then a significant improvement on oxalic acid removal by CNT catalytic ozonation is obtained. The heat treatment of CNT under H2 atmosphere is more effective in eliminating acidic groups and increasing basic groups than the case of N2 atmosphere at the same temperature, which results in higher catalytic activity and lower total organic carbon (TOC) release in ozonation correspondingly. A linear relationship is observed between the pH at the point of zero charge (pHPZC) of CNT and the rate constant for ozonation of oxalic acid in the presence of CNT with different treatments. It is suggested that heat treatment can increase the basic property of CNT, which can enhance the contribution of surface reactions to the whole reactions for ozonation of oxalic acid. [ABSTRACT FROM AUTHOR]

Abstract: The catalytic activity of FeOOH on ozonation of oxalic acid at pH 4.0 and 7.0 conditions was investigated in a semi-continuous experimental mode. The results indicate that FeOOH can effectively promote the generation of hydroxyl radicals ( acidic and neutral pH conditions, resulting in the enhancement of the degradation efficiency of oxalic acid by ozone. It is deduced that the hydroxyl groups both of in neutral state (Me-OH) and positive charge state (Me-OH2 +) can perform as the active sites for ozone decomposition into hydroxyl radicals generation. The ligand exchange of hydroxyl groups by phosphate adsorption deteriorates the catalytic activity of FeOOH on ozonation, but the phosphate is found to desorb from FeOOH during the catalytic ozonation process, resulting in the reactivation of the catalytic activity of FeOOH. [Copyright &y& Elsevier]

Abstract: A study has been conducted on the decomposition of 2-chlorophenol (2-CP) applying a heterogeneous Fenton reaction using goethite as catalyst at pH 3. The research was aimed at obtaining a workable kinetic expression apt for developing a kinetic model for scaling up purposes. Several aspects of the reaction have been described in the available literature but, for the moment, without a reasonable representation of the entire reaction behavior. In order to provide a more comprehensive and probable explanation of the whole observed performance, a set of experiments was carried out varying systematically all the significant variables. The proposal considers that the reaction is essentially a combination of four heterogeneous processes associated with one typical homogeneous Fenton reaction. Three of the surface reactions explain a very small iron leaching to the medium by a proton induced solubilization, a reductive dissolution reaction and a non-reductive iron release produced by detected 2-CP chemical decomposition byproducts, particularly, chlorohydroquinone (ClHQ) and oxalic acid (OxA). Iron concentration in the solution may be further increased in the final stages of the reaction after most of the 2-CP has been degraded, by the appearance of OxA that takes part in a third surface reaction. The fourth heterogeneous reaction rationalizes the unusual hydrogen peroxide consumption at high catalyst loadings. During the homogeneous reaction, the presence of ClHQ and ClBQ produces a homogeneous autocatalytic beneficial enhancement of the Fe3+ →Fe2+ transformation. Consequently, the existence of phenolic derivatives either in the mixture or as reaction byproducts produces a beneficial enhancement of the reaction rate. Very low iron leaching is required to produce the onset of the homogeneous Fenton reaction, which was shown to be strongly dependent upon the reaction temperature. All the experimental findings were satisfactorily described by a set of 19-step feasible reaction scheme. The process could be useful for the treatment of wastewaters containing pollutants with phenolic derivatives, as long as iron leaching remains within tolerable limits. [Copyright &y& Elsevier]

Abstract: Multi-walled carbon nanotube (MWCNT) has been used in the catalytic ozonation of oxalic acid in aqueous solution, which was pretreated using ozone and was characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption and Boehm titration. The effect of ozonation pretreatment on the catalytic activity of MWCNT and the ozonation mechanism of oxalic acid in the presence of MWCNT were investigated. The results indicate that with the increasing pretreatment time, the atom ratio of oxygen to carbon and the number of surface acid groups on MWCNT increase, while the catalytic activity of MWCNT on ozonation of oxalic acid decreases, suggesting that the chemical characteristics of MWCNT mainly determine its catalytic activity on oxalic acid mineralization. The inhibition of tert-butyl alcohol on the degradation of oxalic acid is slight for pristine MWCNT catalytic ozonation and this inhibition trend becomes more obvious when MWCNT was pretreated by ozone. A free radical mechanism was proposed which involves both surface reactions and bulk reactions between the oxalic acid and active species. [Copyright &y& Elsevier]

Abstract: The effects of four carboxylic acids: malic, citric, tartaric and oxalic acids on the leaching of iron from two commercial iron oxides (hematite, α-Fe2O3, and magnetite, Fe3O4) have been investigated. The variables studied were the doses of iron oxides and carboxylic acids used as well as aqueous pH, temperature and the presence of hydrogen peroxide and/or UV-A radiation. On the whole, Fe3O4 led to higher amounts of leached iron than α-Fe2O3, and oxalic acid was the most effective carboxylic acid used. The importance of iron leaching has been considered to explain the photodegradation of bisphenol A (BPA) by UV-A/iron oxides systems. The influence of the presence of hydrogen peroxide and/or titania on the efficiency of these oxidation systems was also investigated. At the conditions tested, advanced oxidation with the UV-A/iron oxide/oxalic acid/H2O2/TiO2 system led to the lowest BPA half life (<15min) among those processes studied. [Copyright &y& Elsevier]

Abstract: The electrocatalytic oxidation of o-nitrophenol (o-NP), m-nitrophenol (m-NP) and p-nitrophenol (p-NP) has been studied at Bi-doped lead dioxide anodes on acid medium by cyclic voltammetry and bulk electrolysis. The results of voltammetric studies indicated that these nitrophenol isomers were indirectly oxidized by l in the solutions. Within the present experimental conditions used (50mg of nitrophenol L−1, pH 4.3, 30mAcm−2, 303K), the complete decomposition of nitrophenols (NPs) was achieved. The electrocatalytic oxidation of NPs lay in the order: p-NP> m-NP> o-NP. Molecular configuration including the electron character and hydrogen bonds of NPs significantly influenced the electrocatalytic oxidation of these isomers. Hydroquinone, catechol, resorcinol, benzoquinone, aminophenols, glutaconic acid and maleic acid and oxalic acid have been detected as soluble products during the electrolysis of NPs. The possible degradation pathways of these isomers were proposed. The first stage is the release of nitro group from the aromatic rings. As a consequence, hydroquinone, catechol, resorcinol and benzoquinone are formed. These organic compounds are oxidized initially to carboxylic acids (glutaconic acid, maleic acid and oxalic acid) and later to carbon dioxide and water. Simultaneously, the reduction of NPs to aminophenols takes place at the cathode. [Copyright &y& Elsevier]

Abstract: Solar photo-Fenton and solar photo-Fenton–ferrioxalate processes using a compound parabolic collector (CPC) were applied to the degradation of Reactive Blue 4 (RB4) solutions, proving to be an efficient method. Multivariate experimental design (including the following variables: pH and initial concentrations of Fe(II), oxalic acid, H2O2 and RB4) was used. The efficiency of photocatalytic degradation was determined from the analysis of the following parameters: color removal, total organic carbon (TOC) and chemical oxygen demand (COD). The decoloration rate pseudoconstant was calculated as a function of the accumulated solar energy received by the water solution. Experimental data were fitted using neural networks (NNs) which reproduce experimental data within 86% of confidence and allows the simulation of the process for any value of parameters in the experimental range studied. Analysis of dissolved H2O2 during reaction also helps to explain the scavenger effect and the dye mineralization grade. The solar photo-Fenton–ferrioxalate process increases degradation rate of RB4 since ferrioxalate complexes absorb strongly and a higher portion of the solar spectrum can be used. Although the addition of oxalic acid increases operating costs, it improves the process and it also helps to reduce pH in solution, decreasing charges derived from this operation. Under the optimum conditions, ([H2O2]=120ppm (in two additions), [Fe(II)]=7ppm, [(COOH)2]=10ppm, pH 2.5), color and COD were completely removed whereas TOC was reduced up to 66%. [Copyright &y& Elsevier]

Abstract: The oxidation of hazardous organic compounds leads to the formation of several by-products, being oxalic acid and oxamic acid final oxidation products refractory to ozonation. The present work aimed to study the ozonation of those carboxylic acids in the presence of activated carbon at different solution pH. For comparative purposes, experiments of adsorption on activated carbon, ozonation, and ozonation in the presence of activated carbon were carried out. In order to clarify the reaction mechanism, some experiments were done in the presence of a radical scavenger. With the aim of evaluating the role of the activated carbon surface chemistry during the ozonation, two activated carbon samples were assessed. A significant synergistic effect between ozone and activated carbon was evidenced in the oxidation of oxalic acid. Oxamic acid was found to be refractory to oxidation at pH 7. On the other hand, at pH 3, the mineralization of oxamic acid was significantly enhanced by the presence of activated carbon. Generally, the presence of activated carbon during ozonation increased the rate of degradation of both carboxylic acids leading to mineralization. Best results were achieved with the most basic activated carbon. In both cases, the efficiency of activated carbon promoted ozonation decreases with the increase of solution pH. [Copyright &y& Elsevier]

Abstract: Ethylene diamine tetraacetic acid (EDTA) which is a well-known reagent for its metal extraction efficiency was studied for the first time towards the improvement of the catalytic activity and oxygen storage and release properties (OSC) of severely aged commercial three-way catalysts (TWC) on a laboratory scale. Optimization of the experimental parameters of EDTA-washing procedure of TWC was carried out by varying the washing time, volumetric flow rate, and temperature of EDTA solution. The EDTA-washing procedure of TWC was compared with that of oxalic acid-washing regarding their efficiency in removing P, Pb, S, Ca, Zn, Fe, Cu, Cr, Ni, and Mn, all known TWC contaminants that many of them cause severe deterioration of TWC''s activity and oxygen storage and release properties. EDTA appears to be significantly efficient in removing Pb, Zn, Ca, Mn, Fe, Cu and Ni metal contaminants and sulfur but not of phosphorus (P). Phosphorus-containing species were found to be efficiently removed from the aged TWCs after oxalic acid washing. All regeneration procedures applied led to a significant partial recovery of catalytic activity of TWC (CO, C x H y and NO x conversions) under real exhaust gas conditions (dynamometer tests) due to the removal of large amounts of contaminants accumulated on the aged TWC. The washing procedures using oxalic acid alone or in combination with EDTA led to more significant improvements of both catalytic and OSC performance compared with those of EDTA washing alone. This was due to the ability of oxalic acid to remove P-containing compounds which appear to be one of the main causes of commercial three-way catalyst deactivation. [Copyright &y& Elsevier]

Acid solutions containing up to 1 gl−1 of the drug paracetamol have been treated with ozone alone and ozonation catalyzed with Fe2+, Cu2+ and/or UVA light at 25.0 °C. Direct ozonation yields poor degradation due to the high stability of final carboxylic acids formed, whereas more than 83% of mineralization is attained with the catalyzed methods. Under UVA irradiation, organics can be efficiently destroyed by the combined action of generated H2O2 and UVA light. In the presence of Fe2+ and UVA light, the process is accelerated due to the production of oxidant hydroxyl radical (᛫OH) and the photodecomposition of Fe3+ complexes. The highest oxidizing power is achieved by combining Fe2+, Cu2+ and UVA light, because complexes of final acids with Cu2+ are more quickly degraded than those competitively formed with Fe3+. For all catalyzed methods, the initial mineralization rate is enhanced and the percent of degradation generally drops with increasing drug concentration. The paracetamol decay always follows a pseudo-first-order reaction with slightly higher rate constant for catalyzed systems than direct ozonation. Aromatic products such as hydroquinone, p-benzoquinone and 2-hydroxy-4-(N-acetyl)aminophenol are identified by gas chromatography–mass spectrometry (GC–MS) and reversed-phase chromatography. Acetamide is generated when hydroquinone is produced. These products are degraded to oxalic and oxamic acids as ultimate carboxylic acids, as detected by GC–MS and ion-exclusion chromatography. Oxalic acid is generated via glycolic, glyoxylic, tartronic, ketomalonic and maleic acids. While Fe3+-oxalato complexes are photolyzed by UVA light, Cu2+-oxalato, Fe3+-oxamato and Cu2+-oxamato complexes are oxidized with ᛫OH. NH4+ and NO3− ions are produced during mineralization. [Copyright &y& Elsevier]

Abstract: A Fe on activated carbon catalyst has been prepared and tested for phenol oxidation with H2O2 in aqueous solution at low concentration (100mg/L). Working at 50°C, initial pH 3 and a dose of H2O2 corresponding to the stoichiometric amount (500mg/L) complete removal of phenol and a high TOC reduction (around 85%) has been reached. Oxidation of phenol gives rise to highly toxic aromatic intermediates which finally disappear completely evolving to short-chain organic acids. Some of these last showed to be fairly resistant to oxidation being responsible for the residual TOC. In long-term continuous experiments the catalyst undergoes a significant loss of activity in a relatively short term (20–25h) due to Fe leaching, this being related with the amount of oxalic acid produced. Deactivation may also be caused by active sites blockage due to polymeric deposits on whose formation some evidences were found. Washing with 1N NaOH solution allows to recover the activity although complete restoration was not achieved. [Copyright &y& Elsevier]

Abstract: The kinetics of photocatalytic degradation of four different model organic compounds, formic acid (FA), oxalic acid (OA), 4-chlorophenol (4-CP) and the herbicide monuron (3-(4-chlorophenyl)-1,1-dimethylurea) in a self-constructed batch-mode plate photoreactor with a thin flow of contaminated aqueous solution circulating over an illuminated particulate layer of TiO2 P25 (Degussa) was compared. Both OA and FA were adsorbed on TiO2 surface; their mineralization, induced by direct transfer of photogenerated holes, proceeded in a single step, without observable intermediates, following approximately zero order kinetics. Numerical simulations were performed using a newly proposed kinetic model based on the photostationary state assumption. The model allowed an explanation of the observed reaction order as well as the comparison of independent with competitive adsorption of organic compound and oxygen on the photocatalyst surface, yielding a better fit for the case of competition. 4-CP and monuron, which were not adsorbed under the conditions used, were degraded through the action of photogenerated hydroxyl radicals. Their degradation proceeded with lower photoefficiency than for the adsorbed compounds (FA and OA). While the mineralization of both 4-CP and monuron followed zero order kinetics, their degradation was close to first order. The different reaction orders were consistently explained using the photostationary state approach. [Copyright &y& Elsevier]

Abstract: The commercially available TiO2-catalyst (Degussa P25) was modified with nanosized platinum and silver particles by the photoreduction method to obtain different noble metal loading (0.5 and 1wt.%). The characterization of the synthesized catalysts was carried out by the BET method, XPS, TEM and the adsorption of the model pollutant. The degradation of oxalic acid has been studied in aqueous solution photocatalyzed by band-gap-irradiated TiO2, modified with nanosized platinum or silver particles. The photocatalytic activity of TiO2, modified with noble metal, is approximately double that of the semiconducting support. The adsorption properties of the catalysts, as well as the noble metal content on the surface of the support, influence the efficiency of the photocatalytic process. The reaction rate of photocatalytic degradation of the oxalic acid follows a zero kinetic order according to the Langmuir–Hinshelwood model. The increase of the quantum yield of the photodestruction reaction of the studied model pollutant is due to the formation of Schottky barriers on the metal–semiconductor interface, which serve as efficient electron traps, preventing the electron–hole recombination. [Copyright &y& Elsevier]