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Obesity causes systemic inflammation, hepatic and renal damage, as well as gut microbiota dysbiosis. Alternative vegetable sources rich in polyphenols are known to prevent or delay the progression of metabolic abnormalities during obesity. Vachellia farnesiana (VF) is a potent source of polyphenols with antioxidant and anti-inflammatory activities with potential anti-obesity effects. We performed an in vivo preventive or an interventional experimental study in mice and in vitro experiments with different cell types. In the preventive study, male C57BL/6 mice were fed with a Control diet, a high-fat diet, or a high-fat diet containing either 0.1% methyl gallate, 10% powdered VFP, or 0.5%, 1%, or 2% of a polyphenolic extract (PE) derived from VFP (Vachellia farnesiana pods) for 14 weeks. In the intervention study, two groups of mice were fed for 14 weeks with a high-fat diet and then one switched to a high-fat diet with 10% powdered VFP for ten additional weeks. In the in vitro studies, we evaluated the effect of a VFPE (Vachellia farnesiana polyphenolic extract) on glucose-stimulated insulin secretion in INS-1E cells or of naringenin or methyl gallate on mitochondrial activity in primary hepatocytes and C2C12 myotubes. VFP or a VFPE increased whole-body energy expenditure and mitochondrial activity in skeletal muscle; prevented insulin resistance, hepatic steatosis, and kidney damage; exerted immunomodulatory effects; and reshaped fecal gut microbiota composition in mice fed a high-fat diet. VFPE decreased insulin secretion in INS-1E cells, and its isolated compounds naringenin and methyl gallate increased mitochondrial activity in primary hepatocytes and C2C12 myotubes. In conclusion VFP or a VFPE prevented systemic inflammation, insulin resistance, and hepatic and renal damage in mice fed a high-fat diet associated with increased energy expenditure, improved mitochondrial function, and reduction in insulin secretion.

In this research work, boron-doped titanium oxide (B-TiO2) was prepared by the sol-gel method to investigate its behavior in the degradation of the recalcitrant hormone estriol (E3). The doped photocatalyst was synthesized at different boron/titania ratios of 2, 3, and 5 wt.% of boron with respect to the TiO2 content. The obtained materials were characterized by UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The textural properties, specific surface area, and porosity were obtained from N2 adsorption–desorption isotherms by BET and BJH methods, respectively. The photocatalytic performance of each synthesized catalyst was evaluated on the degradation of an aqueous solution (10 mg/L) of estriol (E3) under simulated solar radiation. The variation in the hormone concentration was determined by the HPLC technique, and the mineralization was evaluated by the quantification of total organic carbon (TOC). The obtained results indicated that the catalyst with 3 wt.% of boron incorporation exhibited the best performance on the degradation and mineralization of estriol, achieving its complete degradation at 300 kJ/m2 of accumulated energy and 71% of mineralization at 400 kJ/m2 (2 h) obtaining a non-toxic effluent.

A new synthesis method to prepare the heterostructured catalyst MIL-101(Fe) derived Fe2O3 with TiO2 via microwave-assisted sol-gel route followed by pyrolysis was carried out. The mixed oxide catalyst was characterized by high-resolution transmission electron (HRTEM) and scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–Vis DRS spectroscopy, N2 physisorption, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), photoluminescence (PL), and zetametry. The photocatalytic activity was evaluated in the degradation of the nonsteroidal anti-inflammatory drugs (NSAIDs), ibuprofen (IBP), and naproxen (NPX) in a mixture (10 mg/L/each one) at pH 3, using 1 g/L of the catalyst under visible light. The synthesized Fe2O3/TiO2 showed higher surface area, smaller average crystallite size, absorption in the visible range, and narrower band gap than TiO2, which enhanced the photocatalytic performance of TiO2 under visible radiation, allowing 91 and 100% degradation of IBP and NPX within 240 and 15 min of reaction, respectively. Moreover, 79.0% of mineralization of the mixture of NSAIDs in 240 min was achieved using the derived Fe2O3/TiO2 showing good reusability and stability even after three cycles of usage. In the photocatalytic process, holes were the dominant species for NSAIDs degradation.

The photocatalytic activity of boron-doped ZnO with varying concentration (1, 1.5 and 2% wt of B) synthesized by sol-gel method was evaluated on cyanide (CN−) degradation in aqueous solution under simulated solar radiation. The obtained catalysts were characterized by XRD, UV–vis/DRS, ICP-OES, FT-IR, and XPS. The photocatalytic experiments were carried out in a quartz batch reactor using 300 mL of cyanide solution adjusted at pH 11, evaluating different parameters such as the amount of B dopant, catalyst loading and initial concentration of cyanide solution. A 23 central composite faced design was used to maximize CN− photocatalytic degradation. The cyanide concentration was measured by ISE potentiometric method and the content of intermediate ions (OCN−, NO3−, and NH4+) was determined by UV–vis spectrophotometry. The boron incorporation into ZnO lattice (ZnO-B) reduced wurtzite crystallite size (25 nm) and narrowed the band gap (3.0 eV) compared to bare ZnO (43 nm and 3.2 eV, respectively). The ZnO-B 1.5 wt% showed better photocatalytic performance by degrading 89% of a 10 mg L-1 CN− solution compared to 75% that was reached by undoped ZnO; using in both cases 1.4 g L-1 of catalyst loading at accumulated energy of 400 kJ m-2.

In this work, a novel P-doped Fe2O3-TiO2 mixed oxide was successfully prepared by a microwave assisted sol-gel method. The synthesized catalyst was characterized by N2 physisorption, SEM, XRD, XPS, and FTIR, UV–vis DRS, and PL spectroscopies. The iron and phosphorus content in the catalyst samples were quantified by AAS and ICP-OES, respectively. The photocatalytic activity of P-doped Fe2O3-TiO2 powders were evaluated in the photocatalytic degradation of sulfamethazine (SMTZ). The Box Behnken design (BBD) and response surface methodology (RSM) were applied for modeling the effect and optimizing of the operational parameters levels on the degradation percentage of SMTZ. The complete degradation and mineralization percentage of 30% of SMTZ solution at pH 9 was achieved within 300 min of reaction, with the optimum P doping amount of 1.2 wt % and 1.25 g/L of catalyst loading. The 1.2 wt % P-doped Fe2O3-TiO2 mixed oxide showed considerably higher photocatalytic activity than Fe2O3-TiO2 or TiO2. This enhanced performance could be attributed to the small crystallite size, narrow band gap, high specific surface area and increased number of surface hydroxyls on TiO2 nanoparticles. Additionally, the stability and reusability of this catalyst was demonstrated during three cycles of SMTZ degradation.

The presence of emerging contaminants (EC), such as antibiotics in water bodies, is considered an environmental issue. In this work, the iron sources FeC2O4•2H2O (FOD), complexes of iron/oxalate (Fe2+/Ox), and FeSO4 as reference were evaluated as catalysts on the degradation of pyrazinamide (10 mg L−1) antibiotic by the photo-Fenton process. Different parameters were studied such as initial pH value (3, 4.5, and 6), Fe2+/H2O2 molar ratio (1:20, 1:30, and 1:40), and Fe2+/Ox with different molar ratios (1:3, 1:6, and 1:9). The best performance was achieved with a 1:20 Fe2+/H2O2 molar ratio using FeSO4 and FOD showing similar results as FeSO4 catalyst at pH 3 and 4.5. The degradation rate at pH 6 was enhanced using Fe2+/Ox (1:3) compared to FeSO4, and this behavior was explained by Fenton reactants consumption and the oxalate use. The iron source FOD exhibited a poor performance at pH 6 compared with FeSO4; however, FOD activity was notably increased at pH 6 using a greater amount of catalyst, reaching 86.8% of pyrazinamide degradation in 60 min, even higher than using Fe2+/Ox 1:3 complex (68.9%), which makes it a suitable catalyst for the degradation of pyrazinamide by the photo-Fenton process.

Oxcarbazepine (OXC) an antiepileptic drug, has been detected in wastewater treatment plant (WWTP) effluents, surface, and groundwater in concentrations ranged from µg L−1 to ng L−1. The presence of this drug and its transformation products (TPs) in the aquatic environment creates uncertainty concerning the potential risks to aquatic species and living beings. In this work, the removal of OXC from the water was conducted by photolysis process and heterogeneous photocatalysis using different ZnO-based catalysts. The TPs formed in both reactions were monitored by LC-MS/MS and UPLC-qTOF-MS. The results showed that the OXC was entirely degraded after 30 min of photolysis and photocatalytic reactions. The formation of the main TPs was similar in both processes: nine TPs were detected in the photolysis, while ten products were identified during the heterogeneous photocatalysis. The photolysis reaction was the main responsible for the formation of TPs in both processes, nevertheless, these TPs remained during the photolysis treatment, while its rapid decomposition was achieved in the photocatalytic process. Different degradation pathways were elucidated based on the detection of the generated products. The main degradation reactions were hydroxylation of OXC, heterocyclic ring photo-oxidation, intramolecular ring closure, and HO• radical attack, which led the destruction of the parent compound oxcarbazepine.

The preparation of hierarchical porous carbon sponges (HCS) from metal oxide nanoparticle@metal‐organic frameworks is reported. ZnO nanoparticles are partially converted to zeolitic imidazolate framework‐8 (ZIF‐8) crystals in presence of n‐butylamine to obtain ZnO@ZIF‐8 porous hybrids. After direct carbonization, followed by ZnO acidic etching, ZnO@ZIF‐8 crystals were converted to submicrometric HCS. Due to the high surface area and accessible porosity, combining micro‐ and mesoporosity of HCS, their application for the extraction of water pollutants was studied by preparing HCS/polymer membranes, and showed a high efficiency for the fast (650 L m−2 h−1) removal of plastic degradation by‐products (DBP, dibutyl phthalate. DEHP, bis(2‐n‐ethylhexyl)phthalate). DBP and DEHP breakthroughs were lower than 3 % after the filtration of 100 mL of water containing simultaneously both phthalates at a high concentration level (300 μg L−1, each). HCS/polymer membranes were reusable up to 5 times, maintaining their extraction capacity, with relative errors of 6 % for DBP, and

The sulfamethoxazole (SMX) mineralization through the solar photo electro-Fenton (SPEF) process in a pilot plant containing 20 L of 50 mg L−1 SMX solution was investigated. The process was carried out at pH 3 under different operational conditions varying temperature, volumetric flow and applied current density. Box-Behnken experimental design and response surface methodology (RSM) were used to optimize the experimental variables of the SPEF process. Under the optimal conditions, the SPEF was compared with electro-Fenton (EF) and anodic oxidation (AO- H2O2) processes. Under optimum design variables of 47 mA cm−2, 45 °C and 571 L h−1, SPEF was more efficient yielding 90% of TOC removal after 360 min of reaction with a maximum of 83% of mineralization current efficiency (MCE). The main by-products detected on the final solution treated by SPEF were oxalic, maleic, oxamic and fumaric acids, while NH4+ and NO3− were the main inorganic nitrogen ions released during the process.

Nickel-doped TiO2 (0.1, 0.5, 1.0, 2.5, 5.0, and 10.0 wt%) photocatalysts were prepared by the sol–gel method. Physicochemical properties were determined by the characterization using X-ray diffraction, Raman and UV–vis diffuse reflectance spectroscopies, N2 physisorption, and zeta potential determination (PZC). The synthesized materials exhibited the photocatalytically active anatase crystalline phase and the catalysts exhibited stronger absorption in the visible light region with a red shift in the adsorption edge with the increase of Ni doping. The photocatalytic evaluation of TiO2−Ni materials was carried out on p-arsanilic acid (p-ASA, 10 mg L−1) degradation in aqueous suspension under visible radiation. Compared with bare TiO2, the TiO2–Ni 1.0 material (1 wt% Ni-doped TiO2) exhibited higher photocatalytic activity on p-ASA degradation under visible light irradiation allowing a 76% degradation percentage in 180 min reaction time while 60% degradation percentage was achieved with undoped TiO2. The TiO2–Ni 1.0 material showed the highest surface area in comparison with the other prepared materials. Meanwhile, the photocatalytic activity of TiO2–Ni 1.0 can keep even after three cycles with not loss of activity since nickel was not leached from the TiO2-based catalyst into the solution during photocatalytic reaction. Therefore, the doping of the nickel into the TiO2 lattice by the sol–gel method allowed its activation under visible radiation and an efficient photoexcited charge separation to prevent electron-hole recombination showing high chemical stability.

In the present work, an alternative system of 5-hydroxymethylfurfural (HMF) oxidation was studied, in an effort to avoid the use of expensive precious metal catalysts, high pressures and systems not environmentally friendly. The catalysts tested were Co (II), Fe (II) and Cu (II) Salen complexes supported on SBA-15 (Co Salen/SBA-15, Fe Salen/SBA-15 and Cu Salen/SBA-15 respectively). The reaction was carried out in aqueous medium at room temperature (25 °C ± 1) and atmospheric pressure, using hydrogen peroxide (H 2 O 2 ) as the only oxidant agent. The effect of various reaction conditions such as H 2 O 2 content, oxidant agent amount, different transition metals present in the catalyst and temperature were evaluated. The HMF and the reaction products such as; 2,5-diformylfuran (DFF), 2,5-furandicarboxylic acid (FDCA), 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) and 5-formyl-2-furancarboxylic acid (FFCA) were followed by high performance liquid chromatography (HPLC) measurements. The selectivity and reaction kinetics under different reaction conditions was studied. The different synthesized catalysts were extensively characterized by UV–vis spectroscopy, subsequently by FTIR, DR-UV–vis, AA and XPS spectroscopy and through nitrogen physorption, which was related to its catalytic activity. The successful synthesis of SBA-15 support was confirmed by its textural properties and STEM. From the experimental data obtained a reaction mechanism with parallel reactions was proposed founding that the oxidation route of the alcohol group in HMF is favored over of the oxidation of the aldehyde group on the other side of the molecule.

In this research study, WO3/NaNbO3-coupled photocatalysts were synthesized at three WO3 mass ratios (15, 85, and 95 wt%) and characterized. These composites were characterized via X-ray powder diffraction, N2 physisorption, UV–Vis diffuse reflectance spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and photoluminescence techniques. For comparison, bare WO3 and NaNbO3 were also synthesized and characterized. 2,4-Dichlorophenoxyacetic acid (2,4-D) was degraded under visible light to evaluate its photocatalytic performance. The WO3 (95 wt%)/NaNbO3 composite showed higher photocatalytic activity than pure WO3 and NaNbO3 and even than the 15 and 85 wt% coupled materials; thus, the combination with the highest ratio of WO3 with respect to NaNbO3 showed increased photocatalytic activity compared with the bare materials.

In this study, the photocatalytic removal of an emerging contaminant, diclofenac (DCF) sodium, was performed using the nitrogen-doped WO3/TiO2-coupled oxide catalyst (WO3/TiO2-N). The catalyst synthesis was accomplished by a sol–gel method using tetrabutyl orthotitanate (C16H36O4Ti), ammonium p-tungstate [(NH4)10H2W12O42·4H2O] and ammonium nitrate (NH4NO3) as the nitrogen source. For comparison, TiO2 and WO3/TiO2 were also prepared under similar conditions. Analysis by X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance UV–Vis spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS) were conducted to characterize the synthesized materials. The photocatalytic efficiency of the semiconductors was determined in a batch reactor irradiated with simulated solar light. Residual and mineralized DCF were quantified by high-performance liquid chromatography, total organic carbon analysis and ion exchange chromatography. The results indicated that the tungsten atoms were dispersed on the surface of TiO2 as WO3. The partial substitution of oxygen by nitrogen atoms into the lattice of TiO2 was an important factor to improve the photocatalytic efficiency of WO3/TiO2. Therefore, the best photocatalytic activity was obtained with the WO3/TiO2-N0.18 catalyst, reaching 100% DCF transformation at 250 kJ m−2 and complete mineralization at 400 kJ m−2 of solar-accumulated energy.

Photocatalytic degradation of 4-chloro-2-methylphenoxyacetic acid (MCPA) in aqueous solution using Cr(III)-doped TiO2 under UV and visible light was investigated. The semiconductor material was synthesized by a microwave-assisted sol–gel method with Cr(III) doping contents of 0.02, 0.04, and 0.06 wt%. The catalyst was characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), nitrogen physisorption, UV–Vis diffuse reflectance spectroscopy (DRS), and atomic absorption spectroscopy (AAS). The photocatalytic activity for the photodegradation of MCPA was followed by reversed-phase high-performance liquid chromatography (HPLC) and total organic carbon (TOC) analysis. The intermediates formed during degradation were identified using gas chromatography–mass spectrometry (GC–MS). Chloride ion evolution was measured by ion chromatography. Characterization results showed that Cr(III)-doped TiO2 materials possessed a small crystalline size, high surface area, and mesoporous structure. UV–Vis DRS showed enhanced absorption in the visible region as a function of the Cr(III) concentration. The Cr(III)-doped TiO2 catalyst with 0.04 wt% of Cr(III) was more active than bare TiO2 for the degradation of MCPA under both UV and visible light. The intermediates identified during MCPA degradation were 4-chloro-2-methylphenol (CMP), 2-(4-hydroxy-2-methylphenoxy) acetic acid (HMPA), and 2-hydroxybuta-1,3-diene-1,4-diyl-bis (oxy)dimethanol (HBDM); the formation of these intermediates depended on the radiation source.

The improved photocatalyst carbon-doped WO 3 /TiO 2 mixed oxide was synthesized in this study using the sol–gel method. The catalyst was thoroughly characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, N 2 adsorption desorption analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the prepared materials was evaluated with respect to the degradation of sodium diclofenac (DCF) in a batch reactor irradiated under simulated solar light. The progress of the degradation process of the drug was evaluated by high-performance liquid chromatography (HPLC), whereas mineralization was monitored by total organic carbon analysis (TOC) and ion chromatography (IC). The results of the photocatalytic evaluation indicated that the modified catalyst with tungsten and carbon (TWC) exhibited higher photocatalytic activity than TiO 2 (T) and WO 3 /TiO 2 (TW) in the degradation and mineralization of diclofenac (TWC>TW>T). Complete degradation of diclofenac occurred at 250 kJ m −2 of accumulated energy, whereas 82.4% mineralization at 400 kJ m −2 was achieved using the photocatalytic system WO 3 /TiO 2 -C. The improvement in the photocatalytic activity was attributed to the synergistic effect between carbon and WO 3 incorporated into the TiO 2 structure.

Phosphorous-doped Ti-Fe mixed oxide (P-TiO2-αFe2O3) catalysts were prepared by the microwave-assisted sol-gel route and characterized using XRD, SEM, N2 physisorption, UV–vis diffuse reflectance, FTIR, and XPS. P-TiO2-αFe2O3 was evaluated during the degradation of a sulfonamide mixture (5 mg/L, each) under visible light. The photocatalytic process was optimized with a face-centered central composite design. Under optimal conditions (0.5 wt% of αFe2O3, pH 10, and 0.75 g/L of catalyst loading), the sulfate radical advanced oxidation process was carried out using 5 mM K2S2O8 (PS). P doping shifted the light absorption of P-TiO2-αFe2O3 in the visible light range owing to substitutional doping, while the coupling of P-TiO2 with α-Fe2O3 enhanced the absorption in the visible range, which resulted in an increase in the lifetime of the charge carriers and in a superior photoactivity of the P-TiO2-αFe2O3 catalyst in comparison to that of TiO2. The mineralization yield of the sulfonamides (SNs) mixture was enhanced in the presence of an electron acceptor (SO4− ), allowing nearly 69 % within 300 min with the P-TiO2-αFe2O3/PS system, while P-TiO2-αFe2O3 and K2S2O8 oxidation achieved only 27 % and 21 %, respectively. The biodegradability index was 0.48 using the P-TiO2-αFe2O3/PS system, indicating a less toxic effluent than the original compounds. Recycling tests demonstrated that P-TiO2-αFe2O3 exhibits good stability in activating PS for SNs degradation during three cycles. Two main intermediates (pyrimidine and hydroquinone) and their hydroxylated re-arrangements were detected during the degradation of the SNs by the coupled process. Oxalic, oxamic, sulfonic, and acetic acids were also identified as by-products from the degradation of the SNs.

The photocatalytic degradation of a sodium diclofenac (DCF) solution (10 mg/L) under simulated solar radiation was evaluated using a ZnO semiconductor modified by the incorporation of 10, 15, and 20 wt.% fluorine (ZnO-F10, ZnO-F15 and ZnO-F20). The ZnO-F catalysts were synthesized by the sol-gel method using zinc acetate as a precursor of zinc oxide and NH4F as a fluorine source. The photocatalytic performance of the F-doped ZnO material was compared to that of bare ZnO. The obtained photocatalysts were characterized using X-ray diffraction (XRD), Scanning electron microscopy with Energy dispersive spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS) techniques. The Brunauer-Emmett-Teller (BET) surface area, pH of zero charge (pHpzc), and band gap of the solids were also evaluated. An experimental Box-Behnken design combined with response surface methodology was applied to establish the optimal conditions for the photocatalytic degradation of the DCF solution. Complete DCF degradation, total release of chloride ions, and approximately 90% mineralization were achieved during degradation of the drug at an accumulated energy of 400 kJ/m2 under the optimized experimental conditions (1 g/L of ZnO-F20 catalyst with the pH of the DCF solution maintained at 6.5).

The Fe doped TiO2 catalyst was evaluated under visible radiation for As(III) removal. The TiO2–Fe was synthesized by sol–gel technique at 0.0, 1.0, 2.5, 5.0 and 10.0 wt% iron doping concentrations. The semiconductors were characterized by X-ray diffraction, diffuse reflectance UV–vis, Raman spectroscopy, nitrogen physisorption, SEM–EDS and potentiometric titration for point of zero charge determination. The photocatalytic oxidation of As(III) was assessed in aqueous suspension contained 5 mg L−1 As(III) at pH 7 with 0.25 g L−1 catalyst loading. The incorporation of iron ions in TiO2 lattice extended the absorption to visible light region and create surface oxygen vacancies which favor photocatalytic oxidation reaction of As(III) using a small doping amount of Fe (1.0 wt%) in TiO2 powder. Additionally, TiO2–Fe 1.0 showed the highest adsorption capacity for As(V) removal compared to sol–gel TiO2 and P25 indicating that this catalyst is a promising material for As contaminated groundwater treatment.

Mesoporous phosphorous-doped TiO

Cr

In this study, the solar photocatalytic activity of ZnO–Fe2O3 coupled oxide was investigated for the degradation of commercial Dicamba and 2,4-D herbicides. Both pesticides, which are extensively used in agriculture, are active ingredients in water-soluble commercial formulations called Fortune® (480 g/L 3,6-dichloro-2-methoxybenzoic acid, Dicamba) and Hierbamina® (479.5 g/L 2,4-dichlorophenoxyacetic acid, 2,4-D). The catalyst was synthesized via the sol–gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), and Raman spectroscopy. UV-vis diffuse reflectance spectroscopy (DRS) was used to estimate the band gap energy (Eg) of the prepared material. Photocatalytic tests were conducted in a planar reactor operated in batch-mode using a solar light simulator. Complete degradation of both herbicides was attained for a 10 mg/L initial concentration after 300 min using 0.5 g/L of catalyst loading. Oxalic, formic, and acetic acids were the byproducts identified during the degradation of both herbicides. Dechlorination after photocatalytic decomposition was complete for Dicamba. However, only 70% dehalogenation was attained for 2,4-D under simulated solar light.

Cr3+-doped TiO2 nanoparticles (Ti-Cr) were synthesized by microwave-assisted sol-gel method. The Ti-Cr catalyst was characterized by X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy, N2 adsorption-desorption analysis, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, X-ray photoelectron spectroscopy (XPS) and zetametry. The anatase mesoporous Ti-Cr material exhibited a specific surface area of 54.5 m2/g. XPS analysis confirmed the proper substitution of Ti4+ cations by Cr3+ cations in the TiO2 matrix. The particle size was of average size of 17 nm for the undoped TiO2 but only 9.5 nm for Ti-Cr. The Cr atoms promoted the formation of hydroxyl radicals and modified the surface adsorptive properties of TiO2 due to the increase in surface acidity of the material. The photocatalytic evaluation demonstrated that the Ti-Cr catalyst completely degraded (4-chloro-2-methylphenoxy) acetic acid under visible light irradiation, while undoped TiO2 and P25 allowed 45.7% and 31.1%, respectively. The rate of degradation remained 52% after three cycles of catalyst reuse. The higher visible light photocatalytic activity of Ti-Cr was attributed to the beneficial effect of Cr3+ ions on the TiO2 surface creating defects within the TiO2 crystal lattice, which can act as charge-trapping sites, reducing the electron−hole recombination process.

The aim of this work was to apply an experimental response surface methodology (RSM) to optimization of the Acid Yellow 36 (Ay 36) decolorization procedure the electro-Fenton process (EFP) using boron-doped diamond (BDD) electrodes. RSM was used for the evaluation of different operation parameters, process modelling, optimization study, and model prediction analysis. Optimization of the electro-Fenton process for decolorization of 60 mg L −1 of synthetic azo dye solution was analyzed using a central composite design (CCD) in RSM. The response variable for the experimental design was a percentage of the color removal. The three considered factors, at two different levels, were current density ( j = 8 and 23 mA/cm 2 ), catalytic Fe 2+ concentrations (0.1 and 0.3 mmol L −1 ), and electrolysis time (10 and 50 min). According to RSM, the optimum operation conditions were Fe 2+ = 0.24 mmol L −1 , j = 23 mA/cm 2 , and t = 48 min. The maximal decolorization efficiency of 98% was achieved under these conditions.

In this work a comparative study of the catalytic activity of ZnO-Fe2O3 and ZnO-Fe(0) 0.5 wt% materials was carried out in the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) as a commercial formulation Hierbamina®, using a compound parabolic collector (CPC) reactor. The catalysts were synthesized by the sol-gel method and characterized by X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy. The textural properties of solids were determined from N2 adsorption isotherms using the Brunauer-Emmett-Teller (BET) method. The incorporation of Fe(0) onto ZnO was demonstrated by X-ray photoelectron spectroscopy analysis. The photocatalytic tests were performed at pH 7, using 10 mg L(-1) of herbicide and 0.5 g L(-1) of catalyst loading. The decay in herbicide concentration was followed by reversed-phase chromatography. A complete degradation of 2,4-D was achieved using ZnO-Fe(0) while 47% of herbicide removal was attained with ZnO-Fe2O3 mixed oxide for an accumulated energy QUV ≈ 2 kJ L(-1). The removal percentage of total organic carbon (TOC) during the solar photocatalytic process was superior using ZnO-Fe(0), achieving 45% compared to the 15% obtained with the mixed oxide catalyst.

In this work, nitrogen-doped ZnO material was synthesized by the sol-gel method using zinc acetate as the precursor and urea as the nitrogen source (15, 20, 25 and 30% wt.). For comparative purposes, bare ZnO was also prepared. The influence of N doping on structural, morphological, optical and photocatalytic properties was investigated. The synthesized catalysts were characterized by XRD, SEM-EDS, diffuse reflectance UV-Vis spectroscopy, BET and XPS analysis. The photocatalytic activity of N-doped ZnO catalysts was evaluated during the degradation of a mixture of herbicides (2,4-D and picloram) under visible radiation ≥400 nm. The photo-absorption wavelength range of the N-doped ZnO samples was shifted to longer wavelength compared to those of the unmodified ZnO. Among different amounts of dopant agent, the 30% N-doped ZnO material showed higher visible-light activity compared with pure ZnO. Several degradation by-products were identified by using HPLC and ESI-MS/MS. The enhancement of visible photocatalytic activity of the N-doped ZnO semiconductor could be mainly due to their capability in reducing the electron-hole pair recombination.

In this study, a multisyringe chromatography system (MSC) using a C18 monolithic column was proposed for the on-line monitoring of the photocatalytic degradation of isoniazid (INH, 10 mg L −1 ) and pyrazinamide (PYRA, 5 mg L −1 ) mixtures in aqueous solution using a small sample volume (200 μL) with an on-line filtration device in a fully automated approach. During the photocatalytic oxidation using TiO 2 or ZnO semiconductor materials, total organic carbon (TOC) and the formed intermediates were analyzed off-line using ion chromatography, ion exclusion HPLC, and ESI-MS/MS. The results showed that TiO 2 exhibits a better photocatalytic activity than ZnO under UV irradiation (365 nm) for the degradation of INH and PYRA mixtures, generating 97% and 92% degradation, respectively. The optimal oxidation conditions were identified as pH 7 and 1.0 g L −1 of TiO 2 as catalyst. The mineralization of the initial organic compounds was confirmed by the regular decrease in TOC, which indicated 63% mineralization, and the quantitative release of nitrate and nitrite ions, which represent 33% of the nitrogen in these compounds. The major intermediates of INH degradation included isonicotinamide, isonicotinic acid, and pyridine, while the ESI-MS/MS analysis of PYRA aqueous solution after photocatalytic treatment showed the formation of pyrazin-2-ylmethanol, pyrazin-2-ol, and pyrazine. Three low-molecular weight compounds, acetamide, acetic acid and formic acid, were detected during INH and PYRA decomposition. PYRA was more resistant to photocatalytic degradation due to the presence of the pyrazine ring, which provides greater stability against OH attack.

Here, the synergetic effect of coupling solar photoelectro-Fenton (SPEF) and solar heterogeneous photocatalysis (SPC) on the mineralization of 200mL of a 20mg L(-1) atrazine solution, prepared from the commercial herbicide Gesaprim, at pH 3.0 was studied. Uniform, homogeneous and adherent anatase-TiO2 films onto glass spheres of 5mm diameter were prepared by the sol-gel dip-coating method and used as catalyst for SPC. However, this procedure yielded a poor removal of the substrate because of the low oxidation ability of positive holes and OH formed at the catalyst surface to destroy it. Atrazine decay was improved using anodic oxidation (AO), electro-Fenton (EF), SPEF and coupled SPEF-SPC at 100mA. The electrolytic cell contained a boron-doped diamond (BDD) anode and H2O2 was generated at a BDD cathode fed with an air flow. The removal and mineralization of atrazine increased when more oxidizing agents were generated in the sequence AOEFSPEFcoupled SPEF-SPC. Organics were destroyed by OH formed from water oxidation at the BDD anode in AO, along with OH formed from Fenton's reaction between added Fe(2+) and generated H2O2 in EF. In SPEF, solar radiation produced higher amounts of OH induced from the photolysis of Fe(III) species and photodecomposed intermediates like Fe(III)-carboxylate complexes. The synergistic action of sunlight in the most potent coupled SPEF-SPC was ascribed to the additional quick removal of several intermediates with the oxidizing agents formed at the TiO2 surface. After 300min of this treatment, 80% mineralization, 9% mineralization current efficiency and 1.93kWhg(-1) TOC energy cost were obtained. The mineralization of atrazine was inhibited by the production of cyanuric acid, which was the main byproduct detected at the end of the coupled SPEF-SPC process.

The photocatalytic removal of arsenite [As(III)] and monomethylarsonic acid [MMA(V)] was investigated in the presence of UV light (350 nm) and aqueous suspensions of ZnO synthesized by the sol-gel technique. Photocatalytic removal of these potent arsenic compounds results in the effective and rapid mineralization to less toxic inorganic arsenate [As(V)]. The effect of ZnO loading and solution pH on the treatment efficiency of the UV/ZnO photocatalytic process was evaluated. The optimal conditions for the removal of 5 mg L(-1) [As(III)] and [MMA(V)] aqueous solutions were observed at catalyst loadings of 0.25 and 0.50 g L(-1) with solution pH values of 7 and 8, respectively. Under these conditions, the activity of photocatalyst sol-gel ZnO was compared with TiO2 Degussa P25 and commercial ZnO catalyst. The results demonstrate that the high adsorption capacity of ZnO synthesized by sol-gel gives enhanced removal of arsenic species from water samples, indicating that this catalyst is a promising material for treatment of arsenic contaminated groundwater.

The photocatalytic reduction of Cr(VI) from agricultural soil leachates irrigated with Cr(VI)-containing waste hydroponic solution was evaluated in this work. For this purpose, zinc oxide was used as a catalyst under UV irradiation (lambda = 365 nm). The reduction of Cr(VI) was preliminarily evaluated on synthetic solutions with a concentration of 15 mg L(-1) to optimize the catalyst loading and the solution pH and to determine the effect of organic matter. Greater removal of Cr(VI) was observed at pH 7, and the optimum catalyst loading was found to be 2 g L(-1), which achieved an 84% Cr(VI) reduction in 6 h. The influence of dissolved organic matter on the reduction of Cr(VI) was evaluated through the addition of different concentrations of humic acid (HA) to the chromium solution. The removal of Cr(VI) was continuously enhanced as the HA concentration gradually increased from 0 to 14 mg L(-1). The percentage of hexavalent chromium reduction from soil leachates was in the range of 13-99%, and the rate constant was significantly enhanced by the presence of organic compounds in the soil pore water. Thus, a marked synergistic effect between the photocatalytic reduction of Cr(VI) and the organic matter in soil (e.g. humic substances) was observed in real samples and was similar to that observed in the Cr(VI) synthetic solution that contained HA.

In this study, the solar photocatalytic activity (SPA) of WO3/TiO2 photocatalysts synthesized by the sol–gel method with two different percentages of WO3 (2 and 5%wt) was evaluated using malathion as a model contaminant. For comparative purpose bare TiO2 was also prepared by sol–gel process. The powders were characterized by X-ray diffraction (XRD), Raman spectroscopy, diffuse reflectance UV–vis spectroscopy (DRUV–vis), specific surface area by the BET method (SSABET), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy with a high annular angle dark field detector (STEM-HAADF). The XRD, Raman, HRTEM and STEM-HAADF analyses indicated that WO3 was present as a monoclinic crystalline phase with nanometric cluster sizes (1.1 ± 0.1 nm for 2% WO3/TiO2 and 1.35 ± 0.3 nm for 5% WO3/TiO2) and uniformly dispersed on the surface of TiO2. The particle size of the materials was 19.4 ± 3.3 nm and 25.6 ± 3 nm for 2% and 5% WO3/TiO2, respectively. The SPA was evaluated on the degradation of commercial malathion pesticide using natural solar light. The 2% WO3/TiO2 photocatalyst exhibited the best photocatalytic activity achieving 76% of total organic carbon (TOC) abatement after 300 min compared to the 5% WO3/TiO2 and bare TiO2 photocatalysts, which achieved 28 and 47% mineralization, respectively. Finally, experiments were performed to assess 2% WO3/TiO2 catalyst activity on repeated uses; after several successive cycles its photocatalytic activity was retained showing long-term stability.