Apparent Degradation Rate Constant Research Articles

Attenuation of phenylnaphthenic acids related to oil sands process water using solar activated calcium peroxide: Influence of experimental factors, mechanistic modeling, and toxicity evaluation

Refractory naphthenic acids (NAs) are among the primary toxic compounds in oil sands process water (OSPW), a matrix with a complex chemical composition that poses challenges to its remediation. This study evaluated the effectiveness of calcium peroxide (CaO2) combined with solar radiation (solar/CaO2) as an advanced water treatment process for degrading model NAs (1,2,3,4-tetrahydronaphthalene-2-carboxylic acid, pentanoic acid, and diphenylacetic acid) in synthetic water (STW) and provide preliminary insights in treating real OSPW. Solar light and CaO2 acted synergistically to degrade target NAs in STW (>67 of synergistic factor) following a pseudo-first-order kinetic (R2 ≥ 0.95), with an optimal CaO2 dosage of 0.1 g L–1. Inorganic ions and dissolved organic matter were found to hinder the degradation of NAs by solar/CaO2 treatment; however, the complete degradation of NAs was reached in 6.7 h of treatment. The main degradation mechanism involved the generation of hydroxyl radicals (•OH), which contributed ∼90% to the apparent degradation rate constant (K), followed by H2O2 (4–5%) and 1O2 (0–5%). The tentative transformation pathways of three NAs were proposed, confirming an open-ring reaction and resulting in short-chain fatty acid ions as final products. Furthermore, a reduction in acute microbial toxicity and genotoxic effect was observed in the treated samples, suggesting that solar/CaO2 treatment exhibits high environmental compatibility. Furthermore, the solar/CaO2 system was successfully applied as a preliminary step for real-world applications to remove natural NAs, fluorophore organic compounds, and inorganic components from OSPW, demonstrating the potential use of this technology in the advanced treatment of oil-tailing-derived NAs.

Efficient photocatalytic H2O2 production and photodegradation of RhB over K-doped g-C3N4/ZnO S-scheme heterojunction

Designing efficient dual-functional catalysts for photocatalytic oxygen reduction to produce hydrogen peroxide (H2O2) and photodegradation of dye pollutants is challenging. In this work, we designed and fabricated an S-scheme heterojunction (g-C3N4/ZnO composite photocatalyst) via one-pot calcination of a mixture of ZIF-8 and melamine in the KCl/LiCl molten salt medium. KCN/ZnO composite could produce 4.72 mM of H2O2 within 90 min under illumination (with AM 1.5 filter), which is almost 1.3 and 7.8 times than that produced over KCN and ZnO, respectively. Simultaneously, the KCN/ZnO also showed excellent photodegradation performance for the dye pollutants (Rhodamine B, RhB), with a removal rate of 92 % within 2 h. The apparent degradation rate constant of RhB over KCN/ZnO was approximately 5–8 times that of KCN and ZnO. In the photocatalytic process, photo-generated holes and superoxide radicals are the main active species. Oxygen (O2) was mainly reduced to produce H2O2 via a two-electron (2e−) pathway with superoxide radicals as intermediates and the 2e− oxygen reduction reaction selectivity of KCN/ZnO was close to 69.82 %. Photo-generated holes are mainly responsible for the degradation of RhB. Compared with pure KCN and ZnO, the enhanced photocatalytic activity of the KCN/ZnO composite is mainly attributed to the following aspects: 1) larger specific surface area and pore volume is beneficial to expose more active sites; 2) stronger light harvesting ability and red-shifted absorption edge bestow the compound a stronger light utilization efficiency; 3) the construction of S-scheme heterostructure between KCN and ZnO improve the photogenerated electron-hole pairs separation ability and bestow photogenerated carriers a higher redox potential.

Enhanced catalytic activities of natural iron ore in peroxymonosulfate activation assisted by WS2 for rapid degradation of pollutants

The seek for efficient and low-cost heterogeneous catalysts for peroxymonosulfate (PMS) activation holds great promise in the treatment of organic contaminants. Natural iron ore (IO) has been identified as a potential catalyst due to its low environmental risk and cost-savings. Herein, the commercial tungsten sulfide (WS2) was employed to significantly enhance the performance of IO towards PMS activation (WS2/IO/PMS) for the removal of pollutants. This system demonstrated remarkable performance, with >98.2% removal of organic pollutants in 60 min, including dyes and antibiotics, under the optimized conditions of 0.50 g/L IO, 0.10 g/L WS2, 2.0 mM PMS, and initial pH 6.0. The apparent degradation rate constant (k) of Acid Orange 7 (AO7) in WS2/IO/PMS system (0.073 min−1) was about 30.4-fold and 104.3-fold higher than that of in WS2/PMS system (0.0024 min−1) and IO/PMS system (0.0007 min−1), respectively. Mechanism insights revealed the crucial role of WS2 in boosting the degradation kinetics in the WS2/IO/PMS system. The exposed W4+ or S2− species on WS2 surface were the dominant reactive sites responsible for the promotion of Fe3+/Fe2+ redox cycles and subsequently the PMS activation. Importantly, the electrochemical analysis demonstrates that the iron ions released from IO were prone to adsorb onto the WS2 surface, forming active Fe species with high oxidative potential, which remarkably accelerated the electron transfer for Fe2+ regeneration, thereby enhancing PMS activation to generate reactive oxygen species like hydroxyl radicals (OH), sulfate radicals (SO4−) and superoxide radicals (O2−). Furthermore, the practicability of WS2/IO/PMS system was validated by treating various pollutants and investigating the interference of coexisting anions in water. Overall, this study provides a green and advanced strategy to enhance the PMS activation by natural iron ore for efficient water decontamination.

Layered MoS2: effective and environment-friendly nanomaterial for photocatalytic degradation of methylene blue

Photocatalytic degradation is a promising method for removing persistent organic pollutants from water because of its low cost (see solar-driven photocatalysis), high mineralisation of pollutants, and low environmental impact. Photocatalysts based on transition metal dichalcogenides (TMDs) have recently attracting high scientific interest due to their unique electrical, mechanical, and optical properties. A MoS2 photocatalyst of the layered structure was managed to photodegrade methylene blue (MB) under visible light irradiation. The catalyst was thoroughly characterised using SEM, AFM, powder XRD, UV–Vis, Raman, and XPS measurements. The photocatalytic degradation of the MB solution was conducted under the following conditions: (i) reductive and (ii) oxidative. The impact of optical and electronic properties, and the MoS2-MB interaction on photocatalytic activity, was discussed. The apparent rate constants (kapp) of degradation were 3.7 × 10–3; 7.7 × 10–3; 81.7 × 10–3 min−1 for photolysis, oxidative photocatalysis, and reductive photocatalysis. Comparison of the degradation efficiency of MB in reductive and oxidative processes indicates the important role of the reaction with the surface electron. In the oxidation process, oxygen reacts with an electron to form a superoxide anion radical involved in further transformations of the dye, whereas, in the reduction process, the addition of an electron destabilises the chromophore ring and leads to its rupture.

Photoelectrocatalytic Oxidation of Sulfamethazine on TiO2 Electrodes

The photoelectrocatalytic degradation and mineralization of sulfamethazine (SMT), a sulfonamide drug, were explored in aqueous solution. Working electrodes with TiO2 coatings on Ti substrates (TiO2/Ti) were used, which were produced by the dip coating method. TiO2 film electrodes were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) following annealing at 500 °C for 1.5 h. To photoelectrochemically characterize them, photocurrents vs. applied potential curves were used. The photoelectrocatalytic efficiency (PEC) of the TiO2/Ti electrodes regarding the oxidation of SMT has been assessed with reference to degradation and mineralization under different experimental conditions. The selected drug molecule was effectively degraded following the Langmuir–Hinshelwood (L-H) kinetic model. The degradation efficiency was shown to increase with increasing applied potential bias up to +1.5 V vs. Ag/AgCl. It was found to be more favorable in acidic environments compared to alkaline ones. A decrease in the destruction rate constant was recorded when the pH was increased from 3 to 5.6 (natural pH) and 9. The decomposition rate was shown to first increase and subsequently reach a saturation value at high concentrations of SMT, indicating that the degradation also depends on other parameters (e.g., the rate of the charge or the mass transfer on the electrode double layer). The results of the photoelectrocatalytic experiments were compared to those of electrochemical (EC) and photocatalytic (PC) degradation of SMT. A significant enhancement was recorded in the case of the PEC degradation, leading at +1.5 V to an increase of the apparent rate constants of degradation, k, and mineralization, kTOC, of 153 and 298%, respectively, compared to the simple photocatalytic process.

In situ deposition of double Fe-based Fenton catalysts on the porous membrane for the development of multi-defense against various foulants toward highly efficient water purification

Membrane separation technology has been widely employed in wastewater separation, although, it is restricted by terrible membrane fouling. The acceptable “single defense” is insufficient to generate a desirable antifouling surface against various organic foulants in complex wastewater. Therefore, this work designs and constructs a porous surface with “multi-defense” by integrating hydrophilic, underwater superoleophobic, and anti-bacterial nano Fe-based Fenton catalysts of β-FeOOH nanorods and CuFeO2 nanoparticles on the polyvinylidene difluoride membrane via metal-ion-induced deposition process. The obtained composite membrane (MFeOOH/CF) has ultra-stable underwater superoleophobicity and ultra-low oil adhesion, which prevent oils from adhering to the membrane and benefit to separate various surfactant-stabilized oil-in-water emulsions with high water flux and separation efficiency of 99%. MFeOOH/CF also exhibits nearly 100% bactericidal activity against Escherichia coli. Moreover, the various foulants (such as bovine serum albumin, methylene blue, and crude oil) adhered to the membrane after filtration can be successfully degraded by MFeOOH/CF under the solar-driven Fenton process, leading to ultrahigh flux recovery ratio (FRRV) of 98.2 ± 0.3% and a low irreversible fouling ratio (RirV) of 2.0 ± 0.1%. The apparent degradation rate constant (k) of MFeOOH/CF is 2.5 times the β-FeOOH coated membrane (MFeOOH) because the introduction of CuFeO2 nanoparticles provides more reactive sites and lowers the Fe3+/Fe2+ redox potential. This study is working to bring about a highly efficient “multi-defense” on the porous membrane, which will realize membrane regeneration and boost wastewater purification.

Synthesis and Structure-Property Relationships of Novel High Molecular Weight Fully Biobased 2,5-Thiophenedicarboxylic Acid-Based Polyesters.

High molecular weight fully biobased poly(propylene succinate-co-2,5-thiophenedicarboxylate) (PPSTF) random copolyesters based on the emerging biobased aromatic diacid, 2,5-thiophenedicarboxylic acid (TFDCA), in full composition range were synthesized via melt polycondensation. Their crystallization behavior, thermal-mechanical, gas barrier, and biodegradable properties were systematically investigated. A certain level of comonomer cocrystallization was evidenced by XRD, and PTF units had stronger crystallization competitive capability compared to PS units due to the higher stiffness of TFDCA units. These copolyesters exhibited excellent thermal stability, and mechanical properties can be easily controlled by tuning the varied ratio of flexible to rigid segments. Gas barrier properties were studied from both theoretically calculated and experimental perspectives, and the copolyesters even with 50 mol % PS units still showed superior gas permeation resistance. The selected lipase from Aspergillus oryzae can degrade the copolyesters with up to 60 mol % PTF units. The nonbiodegradable-biodegradable transition was found to occur at the number-average sequence length of aromatic PTF units as low as about 3. Interestingly, when compared with their terephthalic acid-based (TA-based) and 2,5-furandicarboxylic acid-based (FDCA-based) analogues with the same content of aromatic units, the apparent degradation rate constant (k) and half period (t1/2) of PPSTF60 were actually between them. These findings offer much promise for the application of polyesters containing odd-carbon diol monomers in green packaging and other fields.

Methylmercury Degradation by Trivalent Manganese.

Methylmercury (MeHg) is a potent neurotoxin and has great adverse health impacts on humans. Organisms and sunlight-mediated demethylation are well-known detoxification pathways of MeHg, yet whether abiotic environmental components contribute to MeHg degradation remains poorly known. Here, we report that MeHg can be degraded by trivalent manganese (Mn(III)), a naturally occurring and widespread oxidant. We found that 28 ± 4% MeHg could be degraded by Mn(III) located on synthesized Mn dioxide (MnO2-x) surfaces during the reaction of 0.91 μg·L-1 MeHg and 5 g·L-1 mineral at an initial pH of 6.0 for 12 h in 10 mM NaNO3 at 25 °C. The presence of low-molecular-weight organic acids (e.g., oxalate and citrate) substantially enhances MeHg degradation by MnO2-x via the formation of soluble Mn(III)-ligand complexes, leading to the cleavage of the carbon-Hg bond. MeHg can also be degraded by reactions with Mn(III)-pyrophosphate complexes, with apparent degradation rate constants comparable to those by biotic and photolytic degradation. Thiol ligands (cysteine and glutathione) show negligible effects on MeHg demethylation by Mn(III). This research demonstrates potential roles of Mn(III) in degrading MeHg in natural environments, which may be further explored for remediating heavily polluted soils and engineered systems containing MeHg.

MIL-53(Fe)@perylene Diimide All-Organic Heterojunctions for the Enhanced Photocatalytic Removal of Pollutants and Selective Oxidation of Benzyl Alcohol

Organic semiconductors are promising materials for the photocatalytic treatment of pollutants and organic synthesis. Herein, MIL-53(Fe)@perylene diimide (PDI) organic heterojunctions were constructed by ultrasonic assembly using PDI as the co-catalyst, and PDI organic supramolecular material was uniformly distributed on the surfaces of MIL-53(Fe). The most effective M53@PDI-20 organic heterojunctions achieved 72.7% photodegradation of rhodamine B (10 mg/L) within 50 min and a 99.9% reduction in Cr(VI) (10 mg/L) for 150 min, and the corresponding apparent degradation rate constants were higher than a single component. Meanwhile, the conversion rate of benzyl alcohol over M53@PDI-20 achieved 91.5% for 5 h with a selectivity of above 90% under visible light exposure, which was more than double that of PDI. The well-matched band structures and the strong π–π bonding interactions between MIL-53(Fe) and PDI can increase the electron delocalization effect to facilitate the transfer and separation of photogenerated carriers. Lots of oxidative reactive species (h+, •O2− and •OH) also played a great contribution to the strong oxidation capacity over the heterojunctions system. This work suggests that MIL-53(Fe)@PDI organic heterojunctions may be a promising material for pollutant removal and organic synthesis.

Density Functional Theory and Machine Learning-Based Quantitative Structure-Activity Relationship Models Enabling Prediction of Contaminant Degradation Performance with Heterogeneous Peroxymonosulfate Treatments.

Heterogeneous peroxymonosulfate (PMS) treatment is recognized as an effective advanced oxidation process (AOP) for the treatment of organic contaminants. Quantitative structure-activity relationship (QSAR) models have been applied to predict the oxidation reaction rates of contaminants in homogeneous PMS treatment systems but are seldom applied in heterogeneous treatment systems. Herein, we established QSAR models updated with density functional theory (DFT) and machine learning approaches to predict the degradation performance for a series of contaminants in heterogeneous PMS systems. We imported the characteristics of organic molecules calculated using constrained DFT as input descriptors and predicted the apparent degradation rate constants of contaminants as the output. The genetic algorithm and deep neural networks were used to improve the predictive accuracy. The qualitative and quantitative results from the QSAR model for the degradation of contaminants can be used to select the most appropriate treatment system. A strategy for selection of the optimum catalyst for PMS treatment of specific contaminants was also established according to the QSAR models. This work not only increases our understanding of contaminant degradation in PMS treatment systems but also highlights a novel QSAR model to predict the degradation performance in complicated heterogeneous AOPs.

Green, zero-waste pathway to fabricate supported nanocatalysts and anti-kinetoplastid agents from sugarcane bagasse

The conversion processes of sugarcane into direct-consumption sugar and juice are generating a tremendous amount of waste, the so-called sugarcane bagasse (SCB). Biochar preparation is among the practical solutions aiming to manage and valorize SCB into high added-value functional material (FM).Herein, we propose a novel zero-waste pathway to fabricate two FMs from one biomass. The SCB was first macerated and ultrasonicated to obtain the natural extract that served as bio-reducing medium. Then, the H2O/EtOH-extracted SCB was in-situ impregnated with a bimetallic solution of copper and silver nitrates. The process produced an intermediate composite (FM0), Ag/Cu-Ag+/Cu2+-loaded SCB which was carbonized to elaborate Ag/Cu-Biochar (FM1), free Ag/Cu nanoparticles (FM2) were obtained by microwaving the residual liquid waste.FM1 exhibited high catalytic activity for the total Fenton-like degradation of methylene blue. The experimental data followed the pseudo-first and the pseudo-second order rate laws with apparent degradation rate constants K1 45 10−3 min−1 and K2 0.115 g.mg−1.min−1, respectively. FM0, FM1 and FM2 were tested as new anti-kinetoplastid materials against two flagellated protozoans namely the Leishmania spp and the Trypanosoma cruzi. Notably, Ag/Cu (FM2) showed exceptional leishmanicidal and trypanocidal effects with IC50 values of 2.909 ± 0.051, 3.580 ± 0.016 and 3.020 ± 0.372 ppm for L.donovani, L. amazonensis and Trypanosoma cruzi, respectively.In this way, we combine green chemistry and agrowaste valorization in a full zero-waste process, to address the 3rd (indicator 3.3.5) and 6th (indicator 6.3.1) United Nations sustainable development goals, ″Good Health and Well-Being″ and ″Clean Water and Sanitation″.

Insights into the Kinetics, Theoretical Model and Mechanism of Free Radical Synergistic Degradation of Micropollutants in UV/Peroxydisulfate Process

The degradation of acyclovir (ACY) and atenolol (ATL) in the UV/peroxydisulfate (UV/PDS) process has been systematically considered, focusing on the degradation kinetics, theoretical models, and reaction pathways via applying a microfluidic UV reaction system. The removal efficiencies of ACY and ATL were >94.8%, and the apparent degradation rate constants (kobs) were 0.0931 and 0.1938 min−1 at pH 6.0 in the UV/PDS system. The sulfate radical (SO4•−) and hydroxyl radical (•OH) were identified as the major reactive radicals. The pH-dependent reaction rate constants of ACY and ATL with •OH and SO4•− were measured via the competing kinetics. Meanwhile, the contributions of •OH and SO4•− for ACY and ATL degradation were calculated by the radical steady-state hypothesis, and the results revealed that SO4•− occupied a decisive position (>84.5%) for the elimination of ACY and ATL. The contribution of •OH became more significant with the increasing pH, while SO4•− was still dominant. Moreover, ACY and ATL degradation performance were systematically evaluated via the experiments and Kintecus model under different operational parameters (Cl−, Br−, HCO3−, NOM, etc.) in the UV/PDS process. Furthermore, the plausible reaction pathways of ACY and ATL were elucidated based on the Fukui function theory and ultra-performance liquid chromatography-tandem quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) analysis. The UV/PDS process has been demonstrated to be an efficient and potential application for micropollutants mitigation.

Nitrogen-doped oxidized activated carbon as efficient metal-free bifunctional material for bisphenol removal: A tuning of surface chemistry

Nitrogen modified oxidized activated carbon (N-OAC) was prepared by nitric acid oxidation and ammonia hydrothermal treatment of activated carbon. The surface functional groups of AC were changed by controlling the synthetic conditions and characterized. It was found that oxygen and nitrogen functional groups was introduced on the surface of AC. The deeper degree of oxidation was in favour of N doping. With well-suited amount of oxygen and nitrogen modification, the adsorption and activation ability toward persulfate could be enhanced simultaneously. The adsorption experiment showed that the maximum adsorption capacity (qm) of N-OAC for bisphenol A (BPA) obtained from a Langmuir isotherm was 147 mg g−1 at 298 K, which was about 1.23 and 1.5 times than that of AC (121 mg g−1) and N-free-OAC (108 mg g−1). N-OAC could also activate persulfate, producing strong oxidizing sulfate radicals. The apparent degradation rate constant of BPA on N-OAC was 0.039 min−1, being about 39 times than that (0.001 min−1) on AC. After adsorption equilibrium within 120 min, the use of N-OAC (240 mg L−1) and persulfate (4 mmol L−1) almost completely removed the added bisphenols (60 mg L−1) at pH 6.6 within 60 min. A synergistic effect and correlation between the adsorption ability, catalytic performance and chemical structures of N-OAC was discussed.

ZIF-8-derived single-atom Cu and N co-coordinated porous carbon as bifunctional material for SMX removal

Single-atom Cu and N co-coordinated porous carbon (Cu-N-C) was synthesized by hydrothermal-calcination using zinc zeolite imidazole frameworks (ZIF-8) as the precursor. The catalyst showed excellent adsorption and catalytic ability due to the ideally-dispersed single atomic copper sites and the unique nitrogen-doped porous carbon. The complete removal of sulfamethoxazole (SMX, 18 mg/L) could be achieved within 40 min of pre-adsorption and 25 min of oxidative degradation in the present of peroxymonosulfate (PMS). The adsorption capacity of Cu-N-C (0.2 g/L) was evaluated to be 58.69 mg/g. The apparent degradation rate constant (k) of SMX on Cu-N-C was 0.155 min-1, which was 14.1 times faster than that on N-C (0.011 min-1). From the activation mechanism, it was found that CuN units acted as the main active sites in Cu-N-C for PMS activation. EPR analysis and quenching experiments verified that the reactive oxygen species (ROSs) of SO4·- and 1O2 were involved in the decomposition and mineralization of SMX. This work provides a new perspective for the development of Fenton-like single-atom catalysts.

Degradation pathways and kinetics of chloroacetonitriles by UV/persulfate in the presence of bromide

Chloroacetonitriles (CANs) are highly toxic nitrogenous disinfection by-products (N-DBPs), which frequently appear in water supply systems and have attracted widespread attention. UV/persulfate (PS) is an effective method to degrade CANs. Bromide (Br−) is widespread in aquatic environments and reacts with oxidative radicals to produce secondary reactive bromine species (RBS), which affects the degradation of CANs by UV/PS. It was found that the degradation of CANs was highly inhibited by Br−. The apparent first-order reaction rate constants of monochloroacetonitrile (MCAN), dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCAN) decreased from 2.63 × 10−3, 2.00 × 10−3 and 8.66 × 10−4 s−1 to 2.58 × 10−4, 1.61 × 10−4 and 1.59 × 10−4 s−1, respectively after adding 20 μM of Br−. HO• was the main radicals contributing to the degradation of CANs when the concentration of Br− was less than 10 μM, compared with SO4•− and direct photolysis. When the concentration of Br− was up to 20 μM, the contributions of RBS accounted for 85.7%, 90.7% and 89.9% of the apparent degradation rate constants of CANs, respectively. During the reaction, about 65% of nitrogen atoms were transformed into NO3− by the CC bond cleavage and oxidation. The yields of Cl− by dechlorination reaction accounted for 83.5%, 71.0% and 41.2% of the chlorine contents in MCAN, DCAN and TCAN, respectively. It was verified that CANs react with free bromine (HOBr) to produce bromochloroacetonitrile (BCAN). DCAN and TCAN are hydrolyzed to produce corresponding haloacetamides (HAMs), which are further reacted with HOBr to produce bromodichloroacetic acid (BDCAA). Furthermore, the generation of bromate was also worth noting via the oxidation of Br− in the UV/PS system.

Hierarchical ZnO/MXene (Nb2C and V2C) heterostructure with efficient electron transfer for enhanced photocatalytic activity

Recently, MXene has attracted much attention as photocatalysts for efficient pollutant degradation in the field of environmental remediation but a rapid recombination of photogenerated carriers usually leads to a decrease in the photocatalytic performance. Constructing a heterostructure is considered as an effective way to improve the catalytic performance of MXene-based photocatalysts due to the promoted interfacial electron transfer. In this work, the chimeric ZnO nanosheets with good carrier mobility were formed on the accordion-shaped MXene (Nb2C and V2C) surface to construct hierarchical ZnO/MXene heterostructure as a photocatalyst for dye degradation. The obtained ZnO/Nb2C and ZnO/V2C hierarchical structure exhibited excellent photocatalytic performance in the degradation of methylene blue (MB): the degradation rate reached 62.62% and 99.53%, respectively, after irradiation with ultraviolet light for 120 min. Also, the apparent degradation rate constants (k) were 0.00777 min−1 and 0.04317 min−1, respectively, which were 2.92 and 16.23 times higher than those of pure ZnO. This was probably attributed to the heterostructures between ZnO and MXene which could shorten the carrier transfer path, which could facilitate the transfer of photo-generated electrons from conduction band (CB) of ZnO to CB of MXene, thereby significantly improving the photocatalytic degradation efficiency. In addition, the ZnO/Nb2C and ZnO/V2C hierarchical structure showed good photocatalytic stability: the degradation rate remained at 58.6% and 97.3%, respectively, after 4 cycles while it only maintained at 22.0% for pure ZnO because the obtained ZnO/MXene hierarchical structure could provide uniform active sites on the surface and porous structure, preventing the aggregation of ZnO or MXene. Therefore, this work could provide a feasible design strategy to improve the catalytic performance of 2D photocatalysts and shed a light on the design of other photocatalysts.

In-situ fabrication of novel BiOCl/Bi5O7I 2D/3D heterostructures with enhanced photocatalytic activity

A novel BiOCl/Bi5O7I (BOC-BOI) heterojunction was prepared by growing ultrathin 2D BiOCl nanosheets in situ on the surface of 3D Bi5O7I microspheres. The 2D/3D heterostructure of BOC-BOI composites inhibited the agglomeration of BiOCl nanosheets, and benefited the multiple reflection and refraction of light, which greatly enhanced the absorption and utilization of light. The 50-BOC-BOI composite showed 97.7% degradation efficiency of rhodamine B (RhB) after 70 min Xe light irradiation. And its apparent degradation rate constant (k) was 0.0377 min−1, being 4.9 and 15.1 times than that of pristine BiOCl (0.0077 min−1) and Bi5O7I (0.0025 min−1), respectively. The enhanced photocatalytic activity of BOC-BOI composites was attributed to stronger light capture ability, more abundant active sites and higher charge carrier separation efficiency, confirmed by UV-Vis DRS, SEM, TEM, BET, Zeta potential and electrochemical characterizations. The free radical capture experiments showed that the main active species in this system were holes (h+) and superoxide free radicals (·O2−). Combining the results of UV-Vis DRS and Mott-Schottky test, a reasonable type II heterojunction mechanism was proposed.

Highly dispersible graphitic carbon nitride: Synthesis and its 2-electron photocatalytic reduction activity of O2

Graphitic carbon nitride (g-CN) is a promising visible light-driven photocatalyst due to its favorable band gap. However, the limited number of active sites and rapid electron-hole recombination largely limit the photocatalytic efficiency of g-CN. This work provides a salt-template method (STM) to produce carbon nitride nanoparticles with high crystalline and dispersibility. 20–50 nm g-CN particles are achieved with high dispersion in aqueous phase, which permits a quasi-homogeneous aqueous photocatalytic oxidation and reduction conditions. It shows excellent photocatalytic activity for H2O2 generation and RhB degradation under visible light. An apparent H2O2 generation rate of 6.32 mmol·g−1·h−1 and an apparent RhB degradation rate constant (kapp) of 0.1707 min−1 were achieved on g-CN from salt-templated method, which are about 32 times and 2 times higher than that of g-CN derived from non-salt-template method, respectively. Increasing the crystallinity as well as reducing the g-CN nanoparticle size were found enhancing the electron-hole separation efficiency and resulting in more active sites. It offers a better and promising photocatalyst for H2O2 generation and organic pollution photodegradation.

Mechanistic investigation of photocatalytic degradation of Bisphenol-A using MIL-88A(Fe)/MoS2 Z-scheme heterojunction composite assisted peroxymonosulfate activation

In this study, a green synthesis method was employed to synthesize MoS2 incorporated MIL-88A(Fe) composite photocatalyst, MIL-88A(Fe)/MoS2 (MSMIL). Its catalytic property was utilized to degrade Bisphenol-A (BPA) in aqueous solution, using peroxymonosulfate (PMS) as oxidant under UV irradiation (intensity: 48 W). Doping of 20 wt% MoS2 was found to produce heterojunction with optimal activity, increased surface area (15.8 m2/g for MIL-88A(Fe) to 78.2 m2/g for MSMIL20) and abundant number of active sites. Insitu formation of intimate heterojunction, coupled with hierarchical porosity, conductive network, and abundant exposed active sites results efficient charge carrier migration to the catalyst surface and accelerates PMS activation to yield highly active radicals. X-ray photoelectron spectroscopy indicates that surface bound Fe3+/Fe2+ and Mo4+/Mo6+ redox interconversions play significant roles in surface adsorbed PMS activation. Scavenging experiments established that both radicalOH·,SO4·-,O2·-and non-radical O21,h+ based degradation pathways were responsible for BPA degradation. The excellent photocatalytic activity was due to the formation of suitable heterojunction which resists e-/h+ recombination, along with formation of an efficient Z-scheme heterojunction. LCMS/MS analysis was employed to determine the intermittent intermediates during BPA degradation and plausible pathways were designed. The apparent degradation rate constant of MSMIL(20)/PMS system was 0.083 min−1 which was 16.6 times and 25.4 times that of PMS alone and MSMIL(20) alone, in presence of UV irradiation. This work elicits critical insights towards synthesizing highly efficient and stable MOF based heterojunction photocatalyst and corresponding mechanistic elucidation of the catalytic activity towards degradative removal of refractory contaminants.

Effects of surface structure and defect behavior on the magnetic, electrical, and photocatalytic properties of Gd-doped CeO2 nanoparticles synthesized by a simple chemical process

Magnetic, electrical, and photocatalytic characteristics of a series of nanoparticles (NPs) of Gd-doped CeO2 (GdxCe1-xO2 (100x% GDC); x = 0.03, 0.05, 0.10, and 0.20) were analyzed in correlation with their surface structure and defect behavior. The GDC NPs were synthesized by a simple chemical process through a polymer-based precursor. X-ray diffraction (XRD) studies confirmed the effective substitution of Gd3+ in the face centered cubic (fcc) lattice of the host matrix of CeO2. The optical band gap (Eg) and oxygen vacancies (VO) increased with Gd-doping as validated by UV–visible reflectance and Raman spectroscopy. Further analysis with X-ray photoelectron spectroscopy (XPS) substantiated the formation of non-stoichiometric CeO2 structure through Ce4+ → Ce3+ reduction to maintain charge neutrality after Gd-doping. Samples of 20% GDC processed at 400 °C, showed the highest saturation magnetization (MS) of 17.58 memu/g at room temperature. A maximum conductivity of 2.11 × 10−3 S/cm was recorded at 650 °C in air in the 20% GDC samples processed at 1100 °C. Using 20% GDC NPs processed at 400 °C, a typical value of apparent degradation rate constant (k) of 2.13 × 10−2 min−1 was obtained for methyl orange (MO) dye under UV–visible irradiation for 10 min.