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The investigation of the pyrolysis behaviour of real-world waste plastics (RWWP) and using them as the feedstock to produce carbon nanotubes (CNTs) could serve as an effective solution to address the global waste plastics catastrophe. This research aimed to characterize the pyrolysis behaviour of RWWP via thermogravimetric analysis (TG) and fast pyrolysis-TG/mass spectrometry (Py-TG/MS) analyses. Activation energies (131.04 kJ mol−1 –171.04 kJ mol−1) for RWWP pyrolysis were calculated by three methods: Flynn-Wall-Ozawa (FWO) method, Kissinger-Akahira-Sunose (KAS) method, and Starink method. Py-TG/MS results indicated that the RWWP could be identified as polystyrene (RWWP-1), polyethylene (RWWP-2), polyethylene terephthalate (RWWP-3, 4), and polypropylene (RWWP-5, 6). In addition, RWWP-1, 2, 5, 6 outperform RWWP-3 and 4 as sources of carbon for producing CNTs. The results showed a high carbon yield of 32.21 wt% and a high degree of CNT purity at 93.04%.

Producing carbon nanotubes (CNTs) from waste plastics could enhance the economic feasibility of the waste management process. Spray pyrolysis is a practical and promising method in this research area. However, the synthesis of CNTs by a spray pyrolysis method is highly reliant on a variety of parameters. Therefore, parameters, including the amount of waste plastics (polypropylene), the catalyst feeding rate and the concentration of the catalyst, and the reaction temperature, were investigated in this work. Results indicate that the reaction factors can influence the carbon deposition and carbon nanotubes yield (CNTs yield). The formed catalyst size played a significant role in the synthesis process. The carbon deposition and CNTs yield reached the top at 21.11 mg g−1plastic and 11.60 mg g−1plastic, respectively, when the PP amount is 2.0 g, the feeding rate of catalyst is 9.0 mL h−1, the concentration of catalyst is 0.2 mol L−1, and the reaction temperature is 800 °C in this work.

In persulfate activation by copper-based catalysts, high-valent copper (Cu(III)) is an overlooked reactive intermediate that contributes to efficient persulfate utilization and organic pollutant removal. However, the mechanisms underlying heterogeneous activation and enhanced persulfate utilization are not fully understood. Here, copper oxide (CuO) nanosheets (synthesized with a facile precipitation method) exhibited high catalytic activity for peroxymonosulfate (PMS) activation with 100% 4-chlorophenol (4-CP) degradation within 3 min. Evidence for the critical role of surface-associated Cu(III) on PMS activation and 4-CP degradation over a wide pH range (pH 3-10) was obtained using in situ Raman spectroscopy, electron paramagnetic resonance, and quenching tests. Cu(III) directly oxidized 4-CP and other phenolic pollutants, with rate constants inversely proportional to their ionization potentials. Cu(III) preferentially oxidizes 4-CP rather than react with two PMS molecules to generate one molecule of

Nitrogen-doped carbon materials attract broad interest as catalysts for peroxymonosulfate (PMS) activation toward an efficient, nonradical advanced oxidation process. However, synthesis of N-rich carbocatalysts is challenging because of the thermal instability of desirable nitrogenous species (pyrrolic, pyridinic, and graphitic N). Furthermore, the relative importance of different nitrogenous configurations (and associated activation mechanisms) are unclear. Herein, we report a "coating-pyrolysis" method to synthesize porous 2D N-rich nanocarbon materials (PCN-x) derived from dopamine and g-C3N4 in different weight proportions. PCN-0.5 calcined at 800 °C had the highest surface area (759 m2/g) and unprecedentedly high N content (18.5 at%), and displayed the highest efficiency for 4-chlorophenol (4-CP) degradation via PMS activation. A positive correlation was observed between 4-CP oxidation rates and the total pyridinic and pyrrolic N content. These N dopants serve as Lewis basic sites to facilitate 4-CP adsorption on the PCN surface and subsequent electron-transfer from 4-CP to PMS, mediated by surface-bound complexes (PMS-PCN-0.5). The main degradation products were chlorinated oligomers (mostly dimeric biphenolic compounds), which adsorbed to and deteriorated the carbocatalyst. Overall, this study offers new insights for rational design of nitrogen-enriched carbocatalysts, and advances mechanistic understanding of the critical role of N species during nonradical PMS activation.

Porous materials have attracted great attention in energy and environment applications, such as metal organic frameworks (MOFs), metal aerogels, carbon aerogels, porous metal oxides. These materials could be also hybridized with other materials into functional composites with superior properties. The high specific area of porous materials offer them the advantage as hosts to conduct catalytic and electrochemical reactions. On one hand, catalytic reactions include photocatalytic, photoelectrocatalytic and electrocatalytic reactions over some gases. On the other hand, they can be used as electrodes in various batteries, such as alkaline metal ion batteries and electrochemical capacitors. So far, both catalysis and batteries are extremely attractive topics. There are also many obstacles to overcome in the exploration of these porous materials. The research related to porous materials for energy and environment applications is at extremely active stage, and this has motivated us to contribute with a roadmap on ‘porous materials for energy and environment applications’.

Existing strategies for bone defect repair are difficult to monitor. Smart scaffold materials that can quantify the efficiency of new bone formation are important for bone regeneration and monitoring. Carbon nanotubes (CNT) have promising bioactivity and electrical conductivity. In this study, a noninvasive and intelligent monitoring scaffold was prepared for bone regeneration and monitoring by integrating carboxylated CNT into chemically cross-linked carboxymethyl chitosan hydrogel. CNT scaffold (0.5% w/v) demonstrated improved mechanical properties with good biocompatibility and electrochemical responsiveness. Cyclic voltammetry and electrochemical impedance spectroscopy of CNT scaffold responded sensitively to seed cell differentiation degree in both cellular and animal levels. Interestingly, the CNT scaffold could make up the easy deactivation shortfall of bone morphogenetic protein 2 by sustainably enhancing stem cell osteogenic differentiation and new bone tissue formation through CNT roles. This research provides new ideas for the development of noninvasive and electrochemically responsive bioactive scaffolds, marking an important step in the development of intelligent tissue engineering.

Peracetic acid (PAA) is considered as an effective and powerful oxidant for eliminating organic contaminants in wastewater treatment. The second-order rate constant (k

Iron minerals, such as iron oxides and iron oxyhydroxides, are the main influential soil components in catalyzed hydrogen peroxide propagation (CHP). Due to their dual effects on H

Lithopone pigments are an important group of white inorganic pigments, with production exceeding 240,000 tons/year in China. Nevertheless, our understanding of its environmental behavior is still limited. In this work, we reported the fast and extensive release of Zn2+ from the commercial lithopone pigment under solar exposure. The lithopone pigment released 40.97% of its total Zn within 24-h simulated sunlight exposure, generating a significant amount of nanoparticles. The commercial lithopone pigment had bandgap energy of 3.63 eV. It can be excited within the solar spectrum (wavelength

Improving the catalytic efficiency of platinum (Pt) for hydrogen evolution reaction (HER) is crucial for water splitting technologies, and hydrogen spillover has emerged as a new frontier in designing the binary-component Pt/support HER electrocatalysts. However, such binary catalysts always suffer from long reaction pathway, undesirable interfacial barrier, and complicated synthesis processes. Here we report a single-phase complex oxide La2Sr2PtO7+δ as a high-performance HER electrocatalysts in acidic media via a unique atomic-scale hydrogen spillover effect between multifunctional catalytic sites. With insights from theoretical calculations, a possible synergistic mechanism involving the hydrogen spillover channel from OLa site→La-Pt bridge site→Pt site is proposed; namely, the OLa site enriches proton, the La-Pt bridge site with thermo-neutral H* adsorption facilitates the hydrogen spillover and H2 generation, and Pt site favors the final H2 desorption. Benefiting from such unusual phenomenon, the resulting La2Sr2PtO7+δ exhibits an exceptional HER electrode activity with low overpotential of 13 mV at 10 mA cm− 2 and small Tafel slope of 22 mV dec− 1, and significantly enhanced intrinsic activity and durability than commercial Pt black catalyst.

Superoxide radicals (O

Photocatalytic production of H2O2 requires simultaneous promotion of the formation and the suppression of the decomposition of H2O2. This work explored a promising strategy of Nafion (perfluorinate...

Photocatalytic production of hydrogen peroxide (H2O2) using water and molecular oxygen as the sole material source is a promising and sustainable solar fuel approach. Herein, we developed an efficient photocatalyst (SN-GQD/TiO2) for H2O2 syntheses by tuning TiO2 with sulfur and nitrogen co-doped graphene quantum dots (SN-GQDs). The high luminescent SN-GQDs homogeneously dispersed on TiO2 surface, which induces the extended visible light absorption and enhanced electron migration. The SN-GQD/TiO2 exhibited 3.2 times H2O2 yield (451 μmol L−1) as that of bare TiO2 under simulated sunlight irradiation, which was also significantly higher than that over GQD/TiO2 and N-GQD/TiO2. Kinetic evaluations suggested that the formation of H2O2 on SN-GQD/TiO2 was dramatically accelerated by 2.4 times compared with that on TiO2, while the decomposition of H2O2 was moderately suppressed (only 25% reduction). The increased H2O2 formation on SN-GQD/TiO2 was attributed to the boosted two-electron reduction of oxygen, which was confirmed by the electron transfer numbers (n = 2.2) obtained from Koutecky-Levuch plots, the less sensitivity of H2O2 production to pH, and the insignificant signals for DMPO–O2 − in ESR measurements. According to theoretical calculations and free energy diagrams of the ORR pathway, a mechanism of proton-coupled electron transfer (PCET) to produce H2O2 was proposed to understand the highly selective two-electron H2O2 production on SN-GQD/TiO2. This study brings an insight to modulate highly selective two-electron photocatalytic reduction of oxygen by introduction of dual doped GQDs that can provide active sites for *OOH formation and proton relays.

Photocatalytic H2O2 production is an innovative on-site H2O2 synthesis method to treat organic pollutants through Fenton-like reactions, avoiding the need and potential liability of H2O2 storage and transportation. Accurate quantification of H2O2 is crucial to explore the mechanism of photocatalytic H2O2 production and optimize reaction parameters. In this work, three common H2O2 quantification methods (i.e., titration with potassium permanganate (KMnO4), and colorimetry with ammonium metavanadate (NH4VO3) or N,N-diethylp-phenylenediamine-horseradish peroxidase (DPD-POD)) were compared and their susceptibility to interference by seven types of representative organics were considered. Interference mechanisms were explored based on the electron-donating (Egap) and electron-accepting (ELUMO) ability of the present organics. The accuracy of the KMnO4 titration method is greatly compromised by aromatic compounds even at 0.1 mM due to the increased KMnO4 consumption by direct oxidation. The presence of p-benzoquinone that directly reacts with NH4VO3 and DPD compromises these colorimetric methods, especially DPD-POD colorimetry at concentrations as low as 0.1 mM. The DPD-POD method should also be scrutinized in the presence of phenols due to significant disturbance by oxidation byproducts (e.g. hydroquinone inducing immediate color disappearance). A flowchart was generated to provide guidelines for selecting an appropriate H2O2 quantification method for different water matrices treated by Fenton-like reactions.

In this study, a comparative activity assessment of several activated carbon (AC) and AC-Fe

Iron minerals, such as iron oxides and iron oxyhydroxides, are the main influential soil components in catalyzed hydrogen peroxide propagation (CHP). Due to their dual effects on H2O2 activation to produce reactive oxygen species (ROS) and invalid consumption to produce oxygen, the intrinsic reactivity of iron minerals toward H2O2 decomposition requires comprehensive investigations. Herein, six iron minerals (hematite, magnetite, maghemite, goethite, feroxyhyte, and ferrihydrite) for H2O2 decomposition were investigated by a combination of normalized kinetic rate constants of H2O2 decomposition (NkH2O2), O2 production (NkO2), benzoic acid degradation (NkBA), and hexachloroethane degradation (NkHCA) over the surface area of each mineral. The results indicate H2O2 decomposition over iron minerals is a surface-related heterogeneous process. Hematite and goethite are the most promising minerals for environmental cleanup in terms of ROS production, because their H2O2 utilization efficiency for benzoic acid (BA) degradation (0.138 and 0.024 mol BA/mol H2O2 for hematite and goethite, respectively) are highest among the six iron minerals. Magnetite and maghemite are highly active for both H2O2 decomposition and O2 production at neutral and basic pHs. The presence of organic compounds suppresses O2 production by more than 60%, which favors H2O2 utilization. Ferrihydrite and feroxyhyte are considered as the problematic mineral for CHP due to that the two minerals acquire a high O2 production and negligible ROS generation at all pHs. The results of this study provide new insights to increase the understandings of H2O2-iron mineral systems and guide the application of iron minerals in chemical oxidation technologies.

The direct conversion of SO

Fenton-like reactions at near neutral pHs are limited by the slow reduction of ferric species. Enhancing generation of from solid peroxides is a promising strategy to accelerate the rate-limiting step. Herein, the H

The incomplete removal of N-nitrosamines in water through current degraded techniques and the carcinogenicity of N-nitrosamines call for alternative complete and safe removal approaches. Here, we describe a cyclic coupling process of photocatalysis and adsorption enabling N-nitrosamines in water thoroughly and safely removed. Among them, the immobilized TiO2/Ti photocatalyst degraded N-nitrosamines into primary and secondary amines up to 100% by attacking on nitrosyl nitrogen via •OH originated from its nanowire film morphology. Furthermore, the affinity of HY zeolite to primary and secondary amines led to efficient adsorption through corresponding to Lagergren adsorption rate equation of second order. And then the cyclic coupling process of photocatalysis and adsorption realized complete and safe removal of N-nitrosamines with various concentration ranging from 0.1 mM to 1 mM in water, significantly higher than the existing reports on the removal rate of N-nitrosamines and the formation potential of N-nitrosamines. This study will lead to new avenues for complete and safe eliminaton of hardly degradable hazardous substances in water.

Superoxide radicals (O2•-) produced by the reaction of Fe(III) with H2O2 can regenerate Fe(II) in Fenton-like reactions, and conditions that facilitate this function enhance Fenton treatment. Here, we developed an efficient Fenton-like system by using calcium peroxide/biochar (CaO2/BC) composites as oxidants and tartaric acid-chelated Fe(III) as catalysts, and tested it for enhanced O2•--based Fe(II) regeneration and faster sulfamethoxazole (SMX) degradation. SMX degradation rates and peroxide utilization efficiencies were significantly higher with CaO2/BC than those with CaO2 or H2O2 lacking BC. The CaO2/BC system showed superior activity to reduce Fe(III), while kinetic analyses using chloroform as a O2•- probe inferred that the O2•- generation rate by CaO2/BC was one-half of that by CaO2. Apparently, O2•- is utilized more efficiently in this system to regenerate Fe(II) and enhance SMX degradation. Additionally, a positive correlation between SMX degradation rate constants and EPR signal intensities of biochar-derived persistent free radicals (PFRs) in CaO2/BC was obtained. We postulate that PFRs enhanced Fe(III) reduction by shuttling electrons donated by O2•-. This represents a new strategy to augment the ability of superoxide to accelerate Fe(III)/Fe(II) cycling for increased hydroxyl radical production and organic pollutant removal in Fenton-like reactions.

One challenge in H2O2 based Fenton-like reaction is to break through the limitation of slow reduction of ferric species (FeIII). Present work describes a dramatic acceleration of Fenton-like reaction at neutral pH by using calcium peroxide (CaO2) as a source of hydrogen peroxide (H2O2) and EDTA as a chelating agent of ferric ions. In an optimized condition, phenol degradation in the H2O2 system displayed an initial latent time of 60 min, while phenol can be degraded immediately and removed completely in 30 min in the CaO2 system. Visual MINTEQ analyses indicated Fe-EDTA− was the active species in the reaction. The contribution of 1O2 in CaO2 system was excluded by the poor selectivity in phenol conversion and the comparable 1O2-TEMP EPR signals in both CaO2 and H2O2 systems. Kinetic analyses using chloroform as the probe of O2·− suggested the high production rate of O2·−, which is four orders of magnitude higher than that in H2O2 system. The mechanism of the accelerated CaO2 based Fenton-like reactions was featured by that two electrons coming from CaO2 can be utilized to promote reduction of FeIII: an inner sphere electron transfer takes place to reduce FeIII-EDTA and produce O2·−, and subsequently O2·− provides an electron to reduce another FeIII-EDTA. The revealed intrinsic reducibility in CaO2 based Fenton-like reaction represents a new strategy to break through the well-known rate limiting step of FeIII reduction in Fenton-like reaction and facilitate the removal of organic pollutants at neutral pHs, and also indicates a promising source of O2·− for diverse applications.

Tetra-amido macrocyclic ligand (TAML) activator is a functional analog of peroxidase enzymes, which activates hydrogen peroxide (H2O2) to form high valence iron-oxo complexes that selectively degrade persistent aromatic organic contaminants (ACs) in water. Here, we develop quantitative structure–activity relationship (QSAR) models based on measured pseudo first-order kinetic rate coefficients ( k obs ) of 29 ACs (e.g., phenols and pharmaceuticals) oxidized by TAML/H2O2 at neutral and basic pH values to gain mechanistic insight on the selectivity and pH dependence of TAML/H2O2 systems. These QSAR models infer that electron donating ability ( E HOMO ) is the most important AC characteristic for TAML/H2O2 oxidation, pointing to a rate-limiting single-electron transfer (SET) mechanism. Oxidation rates at pH 7 also depend on AC reactive indices such as f m i n − and qH+, which respectively represent propensity for electrophilic attack and the most positive net atomic charge on hydrogen atoms. At pH 10, TAML/H2O2 is more reactive towards ACs with a lower hydrogen to carbon atoms ratio (#H:C), suggesting the significance of hydrogen atom abstraction. In addition, ln k obs of 14 monosubstituted phenols is negatively correlated with Hammett constants (σ) and exhibits similar sensitivity to substituent effects as horseradish peroxidase. Although accurately predicting degradation rates of specific ACs in complex wastewater matrices could be difficult, these QSAR models are statistically robust and help predict both relative degradability and reaction mechanism for TAML/H2O2-based treatment processes.

The integrated system of pyrene and cetyltrimethyl ammonium bromide (CTAB) capped silver nanoparticles (AgNPs) with a distance (r) of 2.78 nm has been developed for the detection of Hg (II) and pyrene dimer. The interaction between pyrene and AgNPs results in the fluorescence quenching of pyrene due to the energy transfer, whose mechanism can be attributed to the Forster Resonance Energy Transfer (FRET) supported by experimental observation and theoretical calculations. The developed probe shows a highly selective and sensitive response towards Hg (II) probably due to the amalgam formation, which results in the fluorescence recovery (90%) of pyrene and color change of solution from yellowish brown to colorless. The addition of Hg (II) may increase the distance between pyrene and AgNPs undergoes the ‘FRET OFF’ process. This system gives a selective response towards Hg (II) over other competing metal ions. Under the optimal condition, the system offers good linearity between 0.1 and 0.6 μg mL−1 with a detection limit of 62 ng mL−1. In addition, the system also provides an effective platform for detection of pyrene in its dimer form even at very low concentrations (10 ng mL−1) on the surface of AgNPs. Therefore, it could be used as effective alternatives for the detection of Hg (II) as well as pyrene simultaneously.

The levels, sources and quantitative probabilistic health risks for polycyclic aromatic hydrocarbons (PAHs) in agricultural soils in the vicinity of power, steel and petrochemical plants in the suburbs of Shanghai are discussed. The total concentration of 16 PAHs in the soils ranges from 223 to 8214ng g-1. The sources of PAHs were analyzed by both isomeric ratios and a principal component analysis-multiple linear regression method. The results indicate that PAHs mainly originated from the incomplete combustion of coal and oil. The probabilistic risk assessments for both carcinogenic and non-carcinogenic risks posed by PAHs in soils with adult farmers as concerned receptors were quantitatively calculated by Monte Carlo simulation. The estimated total carcinogenic risks (TCR) for the agricultural soils has a 45% possibility of exceeding the acceptable threshold value (10-6), indicating potential adverse health effects. However, all non-carcinogenic risks are below the threshold value. Oral intake is the dominant exposure pathway, accounting for 77.7% of TCR, while inhalation intake is negligible. The three PAHs with the highest contribution for TCR are BaP (64.35%), DBA (17.56%) and InP (9.06%). Sensitivity analyses indicate that exposure frequency has the greatest impact on the total risk uncertainty, followed by the exposure dose through oral intake and exposure duration. These results indicate that it is essential to manage the health risks of PAH-contaminated agricultural soils in the vicinity of typical industries in megacities.

Although humic acid (HA) can inhibit TiO2 photocatalysis, it can sensitize TiO2 and induce significant visible-light (VL) activity in phenol degradation. This favorable effect of HA was negligible on phosphate-modified TiO2 (P-TiO2), but significantly stronger on Nafion-modified TiO2 (Nf-TiO2). The reaction rate constants for phenol degradation on Nf-TiO2 increased from (0.003±0.001) to (0.025±0.003) min−1 when the reaction was performed in the presence of 20 mg/L HA. The different effects of HA on P-TiO2 and Nf-TiO2 photocatalysis cannot be attributed to adsorption changes, because the adsorption capacities of P-TiO2 and Nf-TiO2 were only slightly lower than that of TiO2 at an initial HA concentration of 20 mg/mL. Scavenger tests, electron paramagnetic resonance spectroscopy, and H2O2 detection were taken to understand the low VL activity of the P-TiO2/HA suspension. The main active species for phenol degradation in the TiO2 and Nf-TiO2 suspensions were superoxide radicals. There were negligible amounts of superoxide radicals in the P-TiO2/HA suspension, possibly because a direct four-electron oxygen reduction reaction occurred. The better VL activity of Nf-TiO2 was rationalized on the basis of Mott–Schottky and electrochemical impedance plots. Nafion modification resulted in cathodic shifts of the energy band positions, increased electron density, and less resistance to electron transfer across the interface between TiO2 and electrolytes. All these factors facilitated electron transfer and improved the production of active species. Phosphate modification therefore did not improve the VL response of HA sensitized TiO2, and low concentrations of HA can facilitate VL photocatalytic degradation of organic pollutants on Nafion surface-modified TiO2.

Rapid hydrogen peroxide (H2O2) decomposition in soils is one of the most important barriers standing in front of catalyzed H2O2 propagations (CHP) for soil and groundwater remediation, and the rates depend greatly on soil components. However, there are lack of indicators to quantitatively evaluate the processes in various soils. Different from previous studies focusing on H2O2 decomposition, O2 production kinetics are more valuable due to the direct relationship with H2O2 utilization. In this contribution, O2 production during H2O2 decomposition in the soil slurry was in situ detected using a fiber-optic oxygen transmitter. A kinetic model of O2 production was developed, which can be fitted well by the measured data of 18 soil samples. A kinetic constant on O2 production (kO2) ranging from 0.001 min−1 to 0.057 min−1 was obtained from the model, which represents the diverse catalytic activity of the soils. The constant kO2 is correlated with the contents of manganese, iron as well as inorganic carbon in the soils, and Mn mineral is the dominant factor. Three types of soils were selected to investigate the effect of acid-washing and stabilizer phosphate addition on phenol oxidation in CHP. Acid-washing can greatly suppress O2 production, while phosphate addition is not desirable for the highly active soils. Phenol slightly inhibits O2 production in the soils with higher kO2 values, which are inverse with those of phenol degradation. Acid-washing can remove Mn minerals but retain most of Fe components, and accordingly increase phenol degradation. Both hydroxyl radicals and superoxide radicals contribute to phenol degradation, and the latter ones display a more significant role. This work increases the understanding of the mechanism of H2O2 decomposition in the soils and provides a parameter (kO2) to guide CHP technologies in soil remediation.