Mineralization Of Organic Pollutants Research Articles

N-coordinated single cobalt atoms catalyst triggering concerted radical-nonradical process in catalytic ozonation for efficient water decontamination

Heterogeneous catalytic ozonation (HCO) has been developed as a promising technology for wastewater treatment, while traditional radical-based HCO process still suffers from insufficient mineralization of organic pollutants. Herein, we constructed a N-coordinated single cobalt atoms catalyst (CoSAC-N-C) triggering concerted radical-nonradical process in catalytic ozonation for efficient decontamination of pollutants. Experiments and theoretical calculations proved that mediate O in O3 obtained electrons from electron-rich N sites for hydroxyl radical (·OH) production, and the terminal O in O3 was attracted on electron-deficient Co sites for nonradical *O generation by O-O cleavage. The synergistic oxidation of ·OH and *O enabled excellent pollutants mineralization, surpassing most of conventional HCO catalysts. CoSAC-N-C exhibited excellent treatment performance for the coking wastewater in a continuous-flow reactor with COD reducing from 86 mg/L to less than 50 mg/L. This work provided a viable strategy of developing dual-site HCO catalysts to promote concerted radical-nonradical oxidations for wastewater treatment.

Heterogeneous CuS QDs/BiVO4@Y2O2S Nanoreactor for Monitorable Photocatalysis.

Exploration of multifunctional integrated catalysts is of great significance for photocatalysis toward practical application. Herein, a 1D confined nanoreactor with a heterogeneous core-shell structure is designed for synergies of efficient catalysis and temperature monitoring by custom encapsulation of Z-scheme heterojunction CuS quantum dots/BiVO4 (CuS QDs/BiVO4) and Y2O2S-Er, Yb. The dispersed active sites created by the QDs with high surface energy improve the mass transfer efficiency, and the efficient electron transport channels at the heterogeneous interface extend the carrier lifetime, which endows the nanoreactor with excellent catalytic performance. Meanwhile, real-time temperature monitoring is realized based on the thermally coupled levels 2H11/2/4S3/2→4I15/2 of Er3+ using fluorescence intensity ratio, which enables the monitorable photocatalysis. Furthermore, the nanoreactor with a multidimensional structure increases effective intermolecular collisions to facilitate the catalytic process by restricting the reaction within distinct enclosed spaces and circumvents potential unknown interaction effects. The design of multi-space nanoconfined reactors opens up a new avenue to modulate catalyst function, providing a unique perspective for photocatalytic applications in the mineralization of organic pollutants, hydrogen production, and nitrogen fixation.

Cyanide-Isolated Cobalt Catalyst for Ultraefficient Advanced Oxidation Treatment.

Catalyst design with a "Co-N-C" structure at the atomic level has shown great interest for peroxymonosulfate (PMS) activation toward advanced oxidation water treatment. Here, we present an innovative way of producing cobalt hexacyanocobaltate (Co-HCC) with an abundance of atomically isolated CoII-NC sites at the outer surface. This material allows ultraefficient PMS activation to generate plenty of sulfate and hydroxyl radicals, with a turnover frequency much higher than those of most cobalt-based catalysts reported so far and even the homogeneous catalysis by Co2+ ions. We gained fundamental insights on its unprecedently high catalytic performance based on experimental results and computational study. Then, we controlled the growth of Co-HCC on a ceramic membrane to form a confined oxidation environment that utilizes the extended surface area and maximal exposure of short-lived radicals for a fast removal of organic pollutants that enter the pores. As a result, this catalytic membrane achieves complete disruption of micropollutants under a water flux up to 10,000 LMH (merely 0.2 s retention time) and further >90% mineralization of organic pollutants in complex industrial wastewater matrices (<100 s retention time), together with the merits of operational simplicity and great longevity (2 weeks continuous run). Our study elicits a new milestone in "Co-N-C" catalyst structure design for PMS activation and highlights the great interest of producing catalytic membranes for a confined treatment of organic pollutants from partial oxidation to complete mineralization as a new benchmark.

Interface engineered Ag-r-GO-CuFe2O4-Fe3O4 heterojunction an efficient photocatalyst for water treatment and toxicity study in Trifolium plants

Herein, we report the Ag-r-GO-CuFe2O4-Fe3O4 nanocomposite (Ag-r-GO-CFO-FO NCs) for effective photocatalytic activity against organic pollutants. Herein the O-S scheme mechanism is achieved by the formation of Ohmic (O) and Schottky (S) junctions. The two interfacial charge carriers for accelerated phono formation and mass transfer and thus increase in the light-harvesting with electron traps for the gerenation of reactive oxygen species (ROS). The photocatalytic activity of the constructed Ag-r-GO-CFO-FO NCs was tested against organic dyes (red RB, orange 2R and black B) and the degradation efficiency was calculated to be 99.8, 99.3 and 99.8% respectively. The radical quenching shows the formation of •OH and O2•- which plays major role in the mineralization of organic pollutants. Total organic carbon (TOC) after the degradation of red RB, orange 2R and black B by Ag-r-GO-CFO-FO NCs was 2.1%, 1.6% and 1.9% respectively, which shows the complete mineralization of the pollutants. In addition, the real-time application of the photocatalytic efficiency of NCs was performed against the effluent collected from dying industrial (which is a combination of red RB, orange 2R and black B) and the degradation efficiency was 98.2%. Toxicity of the NCs was performed against maize plants, the results show that the NCs are non-toxicity towards plants and can be used for real-time application. The efforts provide evidence of the combination of two interfacial charge carriers (O-S scheme) to boost the catalytic activity of the catalyst for water treatment.

Facile tuning Non-radical/Radical oxidation by nitrogen doping on Fe-S doped carbonaceous catalysts for peroxymonosulfate activation

In this paper, iron-sulfur-nitrogen co-doped carbonaceous materials (Fe@SxNyC) was prepared by doping N during the preparation of iron-sulfur co-doped carbonaceous material (Fe@SC), which was used to activate PMS and effectively modulate the radical and non-radical oxidation pathways in the catalytic system to achieve efficient degradation of sulfamerazine (SMR). N doping introduced multiple N sites (graphitic N, pyridinic N and pyrrolic N) in the Fe@SxNyC while promoting the generation of thiophene sulfur of the pristine active sites. Meanwhile, N doping introduced more defects in Fe@S4NC and thus exhibited better catalytic activity than Fe@SC, promoting the decomposition of PMS with a maximum k value (0.1721 min−1). Notably, the involvement of nitrogen shifted the cooperative oxidation reaction from a non-radical (1O2) to a radical-dominated (SO4·–) oxidation pathway with more oxidative intensity, resulting in deeper mineralization of organic pollutants. Moreover, compared with Fe@SC/PMS system, the radical-dominated Fe@S4NC/PMS system had better cycling stability, and the efficiency of SMR degradation could still reach 85 % after 4 cycles. The prepared Fe@S4NC catalytic ceramic membrane exhibited stable water flux and exceptional catalytic activity, demonstrating that Fe@S4NC had good potential for practical applications. This work elucidated the improvement of the catalytic mechanism of iron-carbon based materials by doping with various heteroatoms and provided a theoretical basis to design Fenton-like heterogeneous catalysts suitable for different water matrix.

Fe/Au galvanic nanocells to generate self-sustained Fenton reactions without additives at neutral pH.

The generation of reactive oxygen species (ROS) via the Fenton reaction has received significant attention for widespread applications. This reaction can be triggered by zero-valent metal nanoparticles by converting externally added H2O2 into hydroxyl radicals (˙OH) in acidic media. To avoid the addition of external additives or energy supply, developing self-sustained catalytic systems enabling onsite production of H2O2 at a neutral pH is crucial. Here, we present novel galvanic nanocells (GNCs) based on metallic Fe/Au bilayers on arrays of nanoporous silica nanostructures for the generation of self-sustained Fenton reactions. These GNCs exploit the large electrochemical potential difference between the Fe and Au layers to enable direct H2O2 production and efficient release of Fe2+ in water at neutral pH, thereby triggering the Fenton reaction. Additionally, the GNCs promote Fe2+/Fe3+ circulation and minimize side reactions that passivate the iron surface to enhance their reactivity. The capability to directly trigger the Fenton reaction in water at pH 7 is demonstrated by the fast degradation and mineralization of organic pollutants, by using tiny amounts of catalyst. The self-generated H2O2 and its transformation into ˙OH in a neutral environment provide a promising route not only in environmental remediation but also to produce therapeutic ROS and address the limitations of Fenton catalytic nanostructures.

Interfacial engineering of a multijunctional In2O3/WO3@Ti4N3Tx S-scheme photocatalyst with enhanced photoelectrochemical properties.

Achieving high photoelectrochemical conversion efficiency requires the logical layout of a composite photocatalyst with optimal charge separation and transfer with ideal light harvesting capabilities to enhance the photocatalytic performance and the degradation rate towards organic pollutants. Herein, a novel In2O3/WO3@Ti4N3Tx S-scheme heterojunction was successfully synthesized and confirmed through valence band VB-XPS and Mott Schottky combined analysis. The formed MXene-doped In2O3/WO3@Ti4N3Tx S-scheme significantly enhances the charge flow and spatial separation with an improved oxidation and reduction ability. An in-built interfacial electric field at the WO3-In2O3 boundary enhanced the light-harvesting capacity, whereas Ti4N3Tx MXene offers a unique electron trapping effect which effectively lowers high charge carrier recombination rate-related photocatalytic deficit. It preserves the exceptional redox potency of the photocatalyst by providing a directed acceleration and effective separation of the photogenerated charges. A high carrier density (ND = 7.83 × 1021 cm-3) with a lower negative flat band (VFB = -0.064 V vs. Ag/AgCl) was obtained by Mott-Schottky analysis for 3 wt% In2O3/WO3@Ti4N3Tx, an indicator that a low overpotential is needed to activate photocatalytic reactions. This study, therefore, provides a novel thought for the design and fabrication of an S-scheme heterojunction for photocatalytic reactions for mineralization of organic pollutants in water and clean energy production.

Fabrication of 2D graphene oxide incorporating S-scheme Sn2S3–In2S3 heterojunctions for enhanced photocatalytic mineralization of organic pollutants

Harnessing solar energy using semiconductor-based materials to generate charge pairs to effectively drive photo-redox reactions has been envisioned as a promising approach toward a sustainable future.

Differences among active toluene-degrading microbial communities in farmland soils with different levels of heavy metal pollution.

Heavy metals can severely influence the mineralisation of organic pollutants in a compound-polluted environment. However, to date, no study has focused on the effects of heavy metals on the active organic pollutant-degrading microbial communities to understand the bioremediation mechanism. In this study, toluene was used as the model organic pollutant to explore the effects of soils with different levels of heavy metal pollution on organic contaminant degradation in the same area via stable isotope probing (SIP) and 16S rRNA high-throughput sequencing. Heavy metals can seriously affect toluene biodegradation and regulate the abundance and diversity of microbial communities. SIP revealed a drastic difference in the community structure of active toluene degraders between the unpolluted and heavy metal-polluted soils. All SIP-identified degraders were assigned to nine bacterial classes, among which Alphaproteobacteria, Gammaproteobacteria, and Bacilli were shared by both treatments. Among all active degraders, Nitrospira, Nocardioides, Conexibacteraceae, and Singulisphaera were linked to toluene biodegradation for the first time. Notably, the type of active degrader and microbial diversity were strongly related to biodegradation efficiency, indicating their key role in toluene biodegradation. Overall, heavy metals can affect the microbial diversity and alter the functional microbial communities in soil, thereby influencing the removal efficiency of organic contaminants. Our findings provide novel insights into the biodegradation mechanism of organic pollutants in heavy metal-polluted soils and highlight the biodiversity of microbes involved in toluene biodegradation in compound-polluted environments.

Which Configuration of Photocatalytic Membrane Reactors Has a Major Potential to Be Used at an Industrial Level in Tertiary Sewage Wastewater Treatment?

Photocatalytic membrane reactors (PMRs) have been found to be very effective in the removal of organic pollutants (particularly recalcitrant compounds) from wastewater because they allow for the mineralization of organic pollutants to innocuous by-products, thus achieving high-quality treated water. Owing to the very high volumes of water involved, treated sewage wastewater could be reused if a very efficient tertiary stage, like a PMR, can be foreseen. In this review, the two main PMR configurations (photocatalytic membranes and slurry PMRs) were analyzed as requirements of a tertiary treatment of sewage wastewater considering six design and operational parameters of such plants: (i) continuous wastewater flow rate from the secondary stage; (ii) the self-control of the photodegradation rate related to wastewater chemical–physical parameters; (iii) ability to handle variations of wastewater concentration and flow rate; (iv) the control of the quality of treated wastewater; (v) low plant footprint; and (vi) easy maintenance. In this analysis, some characteristics of photocatalysis (which involves three phases: solid (the photocatalyst), liquid (the wastewater), and gas (oxygen or air)) and those of membranes (they can be produced using different materials and configurations, different processes (pressure-driven or not pressure-driven), etc.) were considered. The obtained results show that slurry PMRs seem more suitable than photocatalytic membranes for such applications. We believe this review can trigger a shift in research from the laboratory to industry in using photocatalytic membrane reactors.

In situ electrogenerated Cu(III) triggers hydroxyl radical production on the Cu-Sb-SnO2 electrode for highly efficient water decontamination

The electrochemical oxidation process has the unique advantage of in-situ •OH generation for deep mineralization of organic pollutants, which is expected to provide a solution for the globally decentralized wastewater treatment and reuse. However, it is still a great challenge to develop low-cost anodes with ultrahigh •OH yield and low energy consumption. Here, a low-cost and stable mixed metal oxide (MMO) anode (Cu-Sb-SnO2) developed by a simple and scalable preparation process presents extremely high organic pollutants degradation efficiency and low energy consumption. The tetracycline degradation kinetics constant of the Cu-Sb-SnO2 system (0.362 min-1) was 9 to 45 times higher than that of other prepared anodes, which is superior to the existing anodes reported so far. The experimental results and theoretical calculations indicate that the Cu-Sb-SnO2 has moderate oxygen evolution potential, larger water adsorption energy, and lower reaction energy barrier, which is conducive to selective water oxidation to generate •OH. Notably, it is systematically and comprehensively confirmed that the generation of •OH triggered by in situ electrogenerated Cu(III) increased •OH steady-state concentration by over four times. Furthermore, the doped Cu species can play a key role in promoting charge transfer as an "electronic porter" between Sn and Sb in the electrocatalytic process by adjusting the electronic structure of the Sb-SnO2 electrode. This work paves the way for the development of MMO anodes utilizing the advantage of the Cu redox shuttle.

Anchoring SrTiO3 nanoparticles on layered ZnIn2S4 to construct S-scheme heterojunctions as novel photocatalysts for efficient degradation of MO dye

Water pollution can be efficiently treated by semiconductor photocatalysts under sunlight irradiation. In this study, novel S-scheme SrTiO3/ZnIn2S4 composites were successfully fabricated via a facile oil-bath method. And the synthesized samples were then characterized by various characterization techniques together with Density Functional Theory (DFT) calculation. The X-Ray Diffraction(XRD)patterns show that SrTiO3/ZnIn2S4 composites are composed of cubic perovskite structure SrTiO3 and hexagonal phase ZnIn2S4. The High Resolution Transmission Electron Microscope(HRTEM)and Field Emission Scanning Electron Microscope (FESEM) images showed the intimate contacts between SrTiO3 and ZnIn2S4 are established to form the heterojunction. The photocatalytic activity of the composite was excellent when degrading organic pollutants, which outperformed that of pristine SrTiO3 and ZnIn2S4. The prepared SrTiO3/ZnIn2S4-33% composite sample was proved to have the best photocatalytic activity, with 98 % degradation of organic pollutants under 32 min. The ·O2– is the main active reaction species for the degradation of organic pollutants, which was demonstrated by free radical trapping experiment. In addition, the mineralization of organic pollutants during the degradation process was analyzed by Total Organic Carbon (TOC) test. According to a series of experimental and theoretical calculations, the S-scheme heterojunction formed in the SrTiO3/ZnIn2S4 composite is put forward for comprehending the photocatalytic degradation of organic pollutants and the formation of free radicals.

Plasmonic photocatalytic degradation of tebuconazole and 2,4-dichlorophenoxyacetic acid by Ag nanoparticles-decorated TiO2 tracked by SERS analysis

Chemical oxidation technologies have been notably used for the mineralization of organic pollutants from aqueous effluents, been especially relevant for the degradation of pesticides. In this context, both tebuconazole (TEB) and 2,4-dichlorophenoxyacetic acid (2,4-D) pesticides were photodegraded by a combined catalyst of TiO2 and silver nanoparticles irradiated by UV-A light (λmax = 368 nm), and the experiments were tracked by surface-enhanced Raman scattering (SERS) spectroscopy. For 2,4-D, the degradation of about 70% was observed after almost 200 min, while for TEB, a decrease of 80% of the initial concentration was observed after approximately 100 min. The SERS monitoring allowed the proposal of some by-products, such as oxidized aliphatic chain and triazole from TEB besides glycolic, glyoxylic and dihydroxyacetic acids from 2,4-D. Their toxicities were predicted through ECOSAR software, verifying that most of them were not harmful to populations of fish, Daphnia and green algae. Thus, the performed oxidative process was efficient in the photodecomposition of TEB and 2,4-D pesticides, inclusive in terms of the decreasing of the toxicity of contaminated effluents.

Novel PWO/ ZnO heterostructured nanocomposites: Synthesis, characterization, and photocatalytic performance

Photocatalytic degradation is becoming an increasingly attractive method for addressing environmental remediation challenges. In this work, the novel pure PWO/ZnO and doped PWO: Er/ZnO: Ag heterostructure nanocomposites with premier photocatalytic efficiency were synthesized via a simple co-precipitation method followed by a solvothermal procedure. X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX), and ultraviolet–visible (UV–Vis) absorbance measurements techniques were employed to characterize the structural and optical properties. HRTEM images prove the possibility of intimate contact formation at the pure and doped PWO/ZnO heterostructure nanocomposite interfaces. The photocatalytic performance of the PWO/ZnO heterostructure nanocomposites in the degradation of the methylene blue (MB) and methyl orange (MO) dyes under UVA light was evaluated. The photocatalysts’ ability in the mineralization of organic pollutants was confirmed by the TOC test. BET and zeta potential analyses were used to study the dye adsorption mechanisms. Additionally, adsorption isotherms and kinetics have been investigated to describe the adsorption of MB and MO into the samples. The degradation rates of MB with PWO/ZnO and PWO: Er/ZnO: Ag heterostructure nanocomposites were 4.7 and 6.6 times higher than those of PWO and PWO: Er nanoparticles. This rate for MO degradation is 5.2 and 3.5 times higher than that of pure PWO and PWO: Er nanoparticles, respectively. This study outlines an easy method to develop innovative, highly effective heterostructure nanocomposites capable of converting UVA light into photocatalytic performance.

High photocatalytic activity and stability of MnV2O6 and Mn2V2O7 synthesized by simple low temperature method for bromophenol blue degradation

Developing an efficient catalyst for Bromophenol blue dye is of great importance for the degradation and mineralization of organic pollutants. Herein, in this study, a hydrothermal approach was used to prepare two different phases of manganese and vanadium mixed oxides, MnV2O6 and Mn2V2O7, and they were used as photocatalysts under visible light. To confirm the structural and morphological properties of MnV2O6 and Mn2V2O7 materials, XRD, SEM-EDS, ICP, BET, XPS, and UV–vis (DRS) were used. The linear fit plot for MnV2O6 and Mn2V2O7 indicates a band gap energy of 1.96 eV and 1.82 eV, respectively. The results revealed that Mn2V2O7 has better photocatalytic performance in bromophenol blue (BPB) degradation than MnV2O6: in 120 min, the BPB exhibits a degradation efficiency of 99.88% for Mn2V2O7 and 96.58% for MnV2O6, and COD was reduced from 41.2 mg/L to 1.37 mg/L for Mn2V2O7 and 4.21 mg/L for MnV2O6, confirming the substantial mineralization of BPB. The Mn2V2O7 preparation method improved its absorption in the visible region, which avoided the rapid charge recombination, and enhanced the electron transfer, resulting in the enhancement of its photocatalytic performance. Furthermore, free radical scavenging tests were carried out and showed that superoxide ions and hydroxyl radicals are responsible for the BPB dye conversion. Finally, this research illustrates a novel insight into designing two different phases of manganese and vanadium mixed oxides, with photocatalytic ability for wastewater treatment.

Band gap-controllable N, P co-doped carbon@ZnxCd1−xIn2S4 for photocatalytic reduction of chromium(VI) and degradation of tetracycline hydrochloride

Construction of carbon-based heterostructural photocatalyst materials with high electron transfer rates is a practical and effective strategy for the mineralization of organic pollutants and removal of toxic metal ions under visible-light irradiation. This study developed a facile hydrothermal route to prepare a series of heterojunction photocatalysts, wherein ZnxCd1-xIn2S4 nanosheets were immobilized on nitrogen and phosphorus co-doped hollow carbon spheres (N, P-C) to form N, P-C@ZnxCd1-xIn2S4 nanocomposites. Comprehensive characterization of the nanocomposites revealed that the tuning of the Zn/Cd molar ratio could effectively modulate the ZnxCd1−xIn2S4 energy band structure. Moreover, Zn0.5Cd0.5In2S4 had the most negative conduction band position and loads on non-metal-doped carbon, with superior carrier transport properties and separation efficiency. N, P-C@Zn0.5Cd0.5In2S4 (N, P-C@ZCIS2) exhibited the best photocatalytic activity for tetracycline hydrochloride degradation and Cr(VI) reduction, with rate constants of 0.04822 mg−1 min−1 and 0.14303 min−1, respectively. Notably, the photocatalysts exhibited good activity and stability even after cycle experiment. This study provides new insights into the design of carbon-based heterojunction photocatalysts for the removal of harmful chemicals.

Efficient mineralization of organic pollutants in water via a phenol-responsive catalytic ozonation process

Background: Catalytic ozonation process has become one of the most promising technologies in organic wastewater treatment industry due to its high efficiency and rapidity. Some researchers have found that alkaline earth metal oxides can be used to promote the ozonation process to removal organic compound in wastewater. And some of them believe that calcium-based catalysts can effectively catalyze the ozonation reaction, but there are few reports about its reaction mechanism.Methods: In this work, calcium oxide was used as catalyst to study their effect in phenol wastewater and the mechanism of catalytic reaction process. In the catalytic ozonation process, the surface hydroxyl of solid CaO-based catalyst can react as the reaction active sites to promote the formation of free radicals, and the Ca2+ solutes in this system can promote the decomposition of H2O2 to produce free radicals. At the same time, the addition of calcium oxide-based catalyst also increases the pH of the reaction system, which is conducive to the decomposition of ozone to produce hydroxyl radicals. Owing to the presence of •OH, 1O2 and •O2−, phenol and by-product are decomposed effectively.Significant findings: The experimental results show that the COD removal rate of phenol reached ∼100% in 20 min. And in this study, the mechanism of CaO-based catalysts used in the ozonation process was studied. We found that both of Ca2+ in solution and solid calcium oxide promoted the formation of active free radicals in catalytic ozonation process.

Highly-efficient degradation of organic pollutants by oxalic acid modified sludge biochar: Mechanism and pathways

The application of sludge biochar (SC) materials as efficient catalysts for organic pollutants mineralization via advanced oxidation process meets the good strategy of “make waste profitable”. The catalytic oxidations of methyl orange (MO) and pyrene by oxalic acid modified sludge biochar (SC-OA) with and without H2O2 were carried out. The analysis of Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), electronic paramagnetic resonance spectrometer (EPR) and free radical quenching experiment were performed and the definite relationships between persistent free radicals (PFRs) type and specific reactive oxygen species (ROS) were made clear. It is suggested for the first time that carbon-centered type PFRs in SC-OA without H2O2 could form O2•- and •OH from COOH groups, while oxygen-centered type PFRs induced H2O2 to produce •OH. The degradation intermediates of MO and pyrene were identified and the transformation pathways were proposed. SC-OA, possessing good sustainable utilization and clean catalytic property, is expected to be popularized and applied in the mineralization of organic pollutants, especially in the in-situ remediation of contaminated soil where is no continuous supply of H2O2.

Copper tungstate (CuWO4)/graphene quantum dots (GQDs) composite photocatalyst for enhanced degradation of phenol under visible light irradiation

Photocatalysis is one of the most preferred methods for the degradation of organic pollutants as it can lead to complete mineralization of organic pollutants employing sunlight as an energy source. Until so far enormous number of investigations have been done regarding the development of visible light responsive, stable, and cost effective photocatalysts. In the present work, owing to objectives mentioned above, an attempt was made to develop an efficient, cheaper, and visible light active composite photocatalyst consisting of moderate band gap, CuWO4 with electron conductive graphene quantum dots. A series of photocatalysts was prepared by varying the amount of CuWO4 while keeping the amount of GQDs fixed, and their activity was evaluated for the phenol degradation under visible light irradiation. The prepared photocatalysts were characterized by using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Raman spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, and Photoluminescence (PL) for the evaluation of crystallinity, functional groups, and properties of charge carrier separation, respectively. The maximum efficiency of photodegradation of phenol simulated wastewater was achieved by sample 0.5GCW (optimized sample having 0.5 wt% of CuWO4 with respect to fixed amount of GQDs), 53.41%, as compared to the pure CuWO4 sample, which exhibited 19.08% efficiency. A possible mechanism for enhanced activity of CuWO4 is proposed mainly due to efficient transfer of electrons from CuWO4 to graphene quantum dots. The results show that the graphene quantum dots GQDs with the CuWO4 significantly contributes to the improvement of photocatalytic performance.

Simultaneous removal of As(III) and organics in Fenton fluidized bed: The favorable co-crystallization of As(V) and Fe(III)

This study has demonstrated that the Fenton fluidized bed (FFB) technology could successfully immobilize As ions on the iron-crystallized (IC) carriers, with simultaneous crystallization of ferric and mineralization of organic pollutants. It was found that rapid fluidized immobilization of aqueous As(V) on the IC carriers was through surface favorable bidentate complexion, while the adsorptive removal of As(III) was rather slow. Adding Fe3+ caused competitive complexion and inhibited the As(V) immobilization. However, effective oxidative crystallization of Fe(II) and As(III) in FFB would take place. With the simultaneous generation of As(V) and Fe(III) by rapid •OH oxidation, two different crystalline precursors would be formed on the IC carriers, leading to efficient co-crystallization of As(V)/Fe(III). Recursive Fe(III) crystallization in the FFB continuously provided essential surface hydroxyl groups for capturing As(V), inducing layer-by-layer co-crystallized immobilization As(V)/Fe(III). The long-term continuous-flow treatment of a practical As(III)-containing industrial organic wastewater exhibited effective/stable co-crystallizations of As(V)/Fe(III), as well as COD removal. The FFB technology is expected to be a good option in treating complex industrial wastewater containing heavy metal and recalcitrant organic pollutants.