AO7 Removal Research Articles

Accelerated removal of organic pollutants by biochar-based iron carbon granule-activated periodate in chloride-containing water: The role of active chlorine

Ubiquitous in water environments, the chloride ion (Cl−) can impact the decontamination capacity of an oxidation system. However, minimal studies are available on its effects in periodate (PI)-based advanced oxidation processes. In this study, a novel biochar-based iron-carbon (FeBC) granule was synthesized to activate PI and remove organic pollutants from water containing Cl−. The FeBC/PI/Cl− system (FeBC: 0.5 g/L; PI: 0.5 mM; AO7: 20 mg/L; NaCl: 50 mM) exhibited excellent performance on various organic pollutants, with ＞ 85 % of Acid Orange (AO7) removal over a pH range of 3–10. Within 20 min after the tenth run, approximately 80 % of AO7 was removed. Inorganic ions and natural organic matter had a negligible effect on AO7 removal. Characterization results confirmed that the presence of Cl− enhanced Fe corrosion, thereby improving PI activation efficiency for removing AO7. Electron paramagnetic resonance spectroscopy and active species trapping experiments verified that radicals (•OH and O2•−) and nonradical (1O2, Fe(IV), and electron transfer) oxidation processes participated in the FeBC/PI system. Moreover, the presence of Cl− accelerated •OH, O2•−, 1O2, and Fe(IV) formation and generated active chlorine, such as HOCl. The main pathways involved in the generation of multiple reactive species were evaluated. AO7 degradation pathways were proposed, and numerous intermediates exhibited decreased toxicity. These findings provide new insights for the decontamination of organic contaminants in water containing Cl−.

UV light assisted degradation of acid orange azo dye by ZVI-ZnS and effluent toxicity effects

Azo dyes, the most common synthetic dyes used in the textile industry, are known xenobiotic compounds and recalcitrant to conventional degradation treatments. As consequence, such contaminants are often discharged into the effluents, treating aquatic ecosystems. Among several processes, the use of zero valent iron (ZVI) represents a suitable alternative to degrade organic molecules containing azo bonds. However, its applications are limited by corrosion and loss of reactivity over the time. To overcome these constraints, ZVI has been coupled to a suitable semiconductor (ZnS) to get a catalytic composite (ZVI-ZnS) active under UV light. The present work deals with the degradation of acid orange (AO7), used as model azo dye, by UV/ZVI-ZnS, as one step treatment and in combination with an adsorption process by biochar. The influence of ZVI-ZnS concentration (0.25, 0.5, 1 and 2 g/L) and reaction time (0–160 min) on degradation of AO7 were investigated. Intermediates formation was monitored by ESI-FT-ICR-MS analysis and the effluent toxicity was assessed by using Artemia franciscana. The experimental results showed that the UV/ZVI-ZnS process at 1 g/L of catalyst allowed to achieve a removal of AO7 up to 97% after 10 min. An increase of the dye relative concentrations as well as the toxicity related to intermediates formations has been observed for treatment time higher than 10 min. The total removal of AO7 together with effluent toxicity reduction was obtained only after the combined treatment (UV/ZVI-ZnS + biochar).

A new strategy for enhanced electrochemically activation of persulfate on B and Co co-modified carbon felt in flow-through system for efficient organic pollutants degradation

Electrochemical activation of persulfate (EA-PS) is gradually attracting attention as an emerging method for wastewater treatment. In this study, a novelty flow-through EA-PS system was first attempted for pollutants degradation using boron and cobalt co-doping carbon felt (B, Co-CF) as the cathode. SEM images, XPS and XRD spectra of B, Co-CF were investigated. The optimal doping ration between B and Co was 1:2. Increasing current density, PS concentration and flow rate, decreasing initial pH accelerated the removal of AO7. The mechanism involved in EA-PS were the comprehensive effect of DET, •OH and SO4•-. B, Co-CF cathode for flow-through system was stable with five cycles efficient AO7 decay performance. EA-PS in flow-through system was an efficient method with low cost and efficient pollutants degradation. This work provides a feasible strategy for synergistically enhancing PS activation and promoting the degradation of organic pollutants.

Confined highly dispersed trace cobalt species in shell porous carbon for activating peroxymonosulfate: Role of superoxide radical and singlet oxygen

The high cobalt leaching of cobalt-based catalysts during the activation of PMS is one of the bottlenecks in SR-AOPs. Herein, a series of trace cobalt confined in carbon shell catalysts (HDCo@C-X) with well-defined structures were designed using NH2-SiO2 nanospheres as a template via the surface-grafting−anchoring method, which was the innovation of the catalysts. AO7 removal rates were in an order of HDCo@C-700 (100%) ≈ HDCo@C-800 (100%) > HDCo@C-600 (80.4%) > Co/C-700 (43.8%). The apparent rate constant of AO7 in HDCo@C-700/PMS (0.0691 min−1) was 8.03 times higher than that of Co/C-700/PMS (0.0086 min−1). The synergistic index (SI) value was introduced to characterize the synergistic relationship between the active sites and confined structures of the catalyst. The SI value of HDCo@C-700/PMS system was 5.2, indicative of a strong synergistic effect between active sites and confined structures. The activation mechanism of HDCo@C-700 for PMS coexisted with free-radical (SO4•−, •OH, and O2•-) and non-radical (1O2 and electron transfer) pathways, and both O2•-and 1O2 played a major role in AO7 degradation. The catalytic activity of HDCo@C-700 gradually decreased to 39.6% and 27.0% for the 2nd and 3rd reuse, respectively, mainly ascribed to the surface oxidation of the carbon shell and the ultra-trace leaching of Co ions. Finally, the intermediates of AO7 in the HDCo@C-700/PMS system were detected by LC-MS, and a possible degradation path was proposed. The in silico toxicity predictions suggested the non-overlooked transformation-derived risks from the degradation products of AO7. This study provides a new insight into the design of PMS activators.

Heterogeneous photo-Fenton degradation of acid orange 7 activated by red mud biochar under visible light irradiation

The heterogeneous photo-Fenton process is an effective technology for degrading organic contaminants in wastewater, and Fe-based catalysts are recently preferred due to their low biotoxicity and geological abundance. Herein, we synthesized a Fe-containing red mud biochar (RMBC) via one-step co-pyrolysis of red mud and shaddock peel as a photo-Fenton catalyst to activate H2O2 and degrade an azo dye (acid orange 7, AO7). RMBC showed excellent AO7 removal capability with a decolorization efficiency of nearly 100% and a mineralization efficiency of 87% in the heterogeneous photo-Fenton process with visible light irradiation, which were kept stable in five successive reuses. RMBC provided Fe2+ for H2O2 activation, and the light irradiation facilitated the redox cycle of Fe2+/Fe3+ in the system to produce more reactive oxygen species (ROS, i.e., •OH) for AO7 degradation. Further investigation revealed that •OH was the predominant ROS responsible for AO7 degradation in the light-free condition, while more ROS were produced in the system with light irradiation, and 1O2 was the primary ROS in the photo-Fenton process for AO7 removal, followed by •OH and O2•-. This study provides insight into the interfacial mechanisms of RMBC as a photo-Fenton catalyst for treating non-degradable organic contaminants in water through advanced oxidation processes under visible light irradiation.

In-situ synthesis of 3D multifunctional graphene-based layered double oxide composite for the removal of nickel and acid orange

Graphene-like materials as a prevalent two-dimensional (2D) material have attracted tremendous attention in the water remediation field, yet the inherent nature of aggregation limits its macroscopic practical applications. To address the dilemma, a novel in-situ synthesis strategy, i.e., integrated “self-template” and “structure designing”, was proposed in this study. Specifically, the organic layered double hydroxide (3D-LDH) was employed as self-template and carbon source to construct the functional three-dimensional (3D) graphene loading with layered double oxide (G@LDO). In virtue of the special 3D structure and components, G@LDO exhibited preeminent and ultrafast remediation ability toward acid orange (AO7, 1870.15 mg/g) and nickel (II) (Ni2+, 110.10 mg/g). Moreover, G@LDO maintained the exceptional removal of AO7 and Ni2+ in a wide pH range and even in the authentic water matrices. The removal mechanisms were systematically investigated, unveiling that AO7 removal was strongly associated with metal-complexation, memory effect, and π-π electron donor–acceptor (EDA). While for Ni2+ removal, besides ion-exchange interaction with Mg2+ associated with LDO, the other S component induced the vacancy defect provided additional active sites for Ni2+ capture. In addition, the recycle experiments demonstrated that G@LDO kept above 85% after five runs. Overall, this work not only opens a new avenue for the preparation of graphene-like material, but also provided a theoritical guidance for the authentic application on the removal of dyes and heavy metals.

Bioprospecting three newly isolated white-rot fungi from Berbak-Sembilang National Park, Indonesia for biodecolorization of anthraquinone and azo dyes

Abstract. Nurhayat OD, Ardiati FC, Ramadhan KP, Anita SH, Okano H, Watanabe T, Yanto DHY. 2021. Bioprospecting three newly isolated white-rot fungi from Berbak-Sembilang National Park, Indonesia for biodecolorization of anthraquinone and azo dyes. Biodiversitas 22: 613-623. Extensive use of textile dyes without proper wastewater treatment may jeopardize the water environment. In this study, bioprospecting newly isolated white-rot fungi from Berbak-Sembilang National Park for decolorizing four synthetic dyes was investigated. A total of 108 wood-decaying fungi were screened by using selective media, resulting in three isolates as the most promising fungal strains (BRB 11, BRB 73, BRB 81). BRB 81 had the best ability to decolorize 91.4% of AB129 and 77.8% of RB5 within 96 hours while the highest removal of RBBR and AO7 was performed by BRB11 around 60% and 37.6%, respectively. The enzymatic degradation was assumed to involve the decolorization process as laccase activities were observed with the highest around 116 UL-1. Based on molecular identification, these three fungal isolates were identified as Phellinus noxius BRB 11, Ceriporia lacerata BRB 81, and Leiotrametes menziesii BRB 73, respectively. In conclusion, P. noxius BRB 11, L. menziesii BRB 73, and C. lacerata BRB 81 could be used as biological agents in textile wastewater treatment and thus, it is important to conserve them as a part of the biodiversity within the local biosphere reserve.

Functionalizing biochar by Co-pyrolysis shaddock peel with red mud for removing acid orange 7 from water

Biochar modification by metal/metal oxide is promising for improving its adsorption capability for contaminants, especially the anions. However, conventional chemical modifications are complicated and costly. In this study, novel Fe/Fe oxide loaded biochars (RMBCs) were synthesized from a one-step co-pyrolysis of red mud (RM) and shaddock peel (SP), and their potential application for removing anionic azo dye (acid orange 7, AO7) from the aqueous environment was evaluated. Fe from red mud was successfully loaded onto biochars pyrolyzed at 300–800 °C, which presented from oxidation form (Fe2O3) to the reduction forms (FeO and Fe0) with increasing pyrolysis temperature. The RMBC produced at 800 °C with RM:SP mass ratio of 1:1 (RMBC8001:1) exhibited the best capability for AO7 removal (∼32 mg/g), attributed to both adsorption and degradation. The higher surface area of RMBC8001:1 and its greater affinity for AO7 led to the higher adsorption. In addition, RMBC8001:1-induced degradation of AO7 was another key mechanism for AO7 removal. The reduction forms of Fe (FeO or Fe0) in RMBC8001:1 may provide electrons for breaking down the azo bond in AO7 molecules and result in degradation, which is further enhanced in acid conditions due to the participation of readily release of Fe2+ and the available H+ in AO7 degradation. Furthermore, RMBC8001:1 can be easily separated from the treated water by using magnetic field, which significantly benefits its separation in wastewater treatment.

G-C3N4/rectorite as a highly efficient catalyst for peroxymonosulfate activation to remove organic contaminants in water

In recent years, modification of graphite carbon nitride (g-C3N4) has drawn considerable attention because of its catalytic potential. In this study, rectorite was designed as a carrier for g-C3N4, and g-C3N4/rectorite was synthesized via pyrolysis under nitrogen protection. The efficiency of g-C3N4/rectorite for peroxymonosulfate (PMS) activation was evaluated using acid Orange 7 dye (AO7) as a model organic contaminant. Material characterization suggested the successful synthesis of g-C3N4/rectorite. The removal of AO7 was significantly enhanced by the composite, compared to pure g-C3N4, rectorite, or their physical mixture. The g-C3N4 content in the composite affected its catalytic ability, while the g-C3N4/rectorite with 41% g-C3N4 content showed the highest catalytic efficiency. Furthermore, the removal of AO7 was affected by catalyst concentration, oxidant concentration, and solution pH. Notably, under the optimized condition (i.e., 0.8 g/L of g-C3N4/rectorite, 0.20 mg/L of PMS, and 6.0 of pH), an initial concentration of 50 mg/L AO7 was removed to a level below the detection limit (i.e., 0.25 mg/L) within 8 min. A recycling test demonstrated the reusability of the g-C3N4/rectorite in six repeated reactions. Singlet oxygen played a key role in PMS activation, suggesting that the non-radical degraded process is the dominated AO7 removal pathway. The rectorite has a confined effect preventing g-C3N4 from agglomeration, inhibiting the electron-hole recombination, and improve the exposure of active sites such as CO groups, -OH groups, and pyridinic N. Overall, g-C3N4/rectorite is a low-cost and environment-friendly catalyst exhibiting high catalytic activity for PMS activation to remove organic contaminants in water.

Sulfate-loaded layered double oxide: A bifunctional adsorbent for simultaneous purification of metal ion and anionic dye

The design of bifunctional materials based on layered double oxides (LDO) with unique properties for the simultaneous removal of metals and dyes is necessary under the background of water sustainable development, yet remains hugely challenges. Herein, sulfate groups decorated on LDO (S-LDO) derived from LDH containing sodium dodecyl sulfate (SDS) were readily prepared via one-step calcination method, which exhibited favorable removal performance toward acid orange 7 (AO7, 4947.22 mg/g) and Cu(II) (181.80 mg/g) in the single system. In AO7-Cu(II) binary system, the removal capacity of Cu(II) was markedly enhanced, but slightly inhibited for AO7 removal owing to competitive adsorption. Additionally, the environmental condition (e.g., pH and ionic strength) had no influence on both contaminants removal. Multiple adsorption-desorption experiments unveiled the well sustainability of S-LDO. Such excellent removal performance was detailly explained by elemental mapping, XRD, and FT-IR. “Memory effect”, complexation and surface adsorption contributed to AO7 removal. While for Cu(II) removal, the synergistic effect between LDO and SO42− via chemical precipitation as well as the strong affinity of SO42− groups via chemisorption played crucial roles. Besides, the electrostatic interactions and additional N-containing adsorption sites offered by the adsorbed AO7 were responsible for the enhanced Cu(II) removal in the binary system. Overall, this work provides valuable information for designing bifunctional adsorbents based on LDO, with the promising application for simultaneous purification of metal ions and anionic dyes.

Fabrication of ZiF-8 metal organic framework (MOFs)-based CuO-ZnO photocatalyst with enhanced solar-light-driven property for degradation of organic dyes

In this study, CuO-ZnO/ZiF-8 was successfully synthesized with different percentages of ZiF-8 Metal-organic Framework (MOF) via ultrasound assisted precipitation method. The physic-chemical properties of the samples were studied by XRD, FESEM, EDX, BET-BJH, FTIR, DRS, and pH pzc techniques. The results showed that the CuO-ZnO/ZiF-8 (20) sample possesses high photocatalytic activity with 98.1% removal of 80 ppm AO7 in 100 min. It could be attributed to the increases the surface area, the pore volume, and pore diameter, as well as efficient homogenous distribution of active sites due to the use of ultrasound irradiation. Furthermore, the presence of ZiF-8 increases light absorption and reduces the recombination rate of electron-hole pairs. • Successfully synthesis of CuO-ZnO/ZiF-8 by ultrasonic assisted precipitation method. • Promising physicochemical and optical properties of the synthesized nanocomposites. • High photocatalytic activity of CuO-ZnO/ZiF-8 (20) (98.1% degradation of AO7) • Investigation of the effective operating parameters on AO7 photodegradation performance. In this research, novel CuO-ZnO/ZiF-8 metal–organic frameworks (MOFs) photocatalyst with different mass percentages of ZiF-8 were prepared for water purification applications under visible light. The precipitation method was used to synthesize CuO-ZnO/ZiF-8 photocatalysts. Some techniques, including XRD, FESEM, EDX, BET-BJH, FTIR, DRS, and pH pzc, were performed to determine the structural, chemical, and optical properties of the prepared samples. DRS analysis represented that CuO-ZnO/ZiF-8(20) had narrower band gap energy compared to CuO-ZnO and ZiF-8. Also, BET-BJH analysis results showed that CuO-ZnO had a low surface area that impeded the absorption of pollutant molecules. In contrast, the CuO-ZnO/ZiF-8(20) sample, due to the presence of ZiF-8, had a high specific surface area which enabled higher pollutant adsorption on the photocatalyst surface. Moreover, the synthesized samples were evaluated for the solar-light-driven removal of different organic dyes, such as Acid Orange 7, Methylene blue, and Malachite green. The tremendously enhanced photocatalytic activity under the simulated solar light with 98.1% removal of AO7 was observed over CuO-ZnO/ZiF-8(20) sample. Then, the effect of initial solution pH as an essential factor on photocatalytic activity was investigated. Finally, the reaction mechanism of AO7 degradation over CuO-ZnO/ZiF-8(20) was proposed.

Efficient peroxymonosulfate (PMS) activation by visible-light-driven formation of polymorphic amorphous manganese oxides

Heterogeneous sulfate radical-based advanced oxidation processes (SR-AOPs) have been widely reported over the last decade as a promising technology for pollutant removal from wastewater. In this study, a novel peroxymonosulfate (PMS) activator was obtained by visible-light-driven Mn(II) oxidation in the presence of nitrate. The photochemically synthesized manganese oxides (PC-MnOx) were polymorphic amorphous nanoparticles and nanorods, with an average oxidation state of approximately 3.0. It possesses effective PMS activation capacity and can remove 20 mg L−1 acid organic II (AO7) within 30 min. The AO7 removal performance of PC-MnOx was slightly decreased in natural waterbodies and in the presence of CO32-, while it showed an anti-interference capacity for Cl-, NO3- and humic acid. Chemical quenching, reactive oxygen species (ROS) trapping, X-ray photoelectric spectroscopy (XPS), in-situ Raman spectroscopy, and electrochemical experiments supported a nonradical mechanism, i.e., electron transfer from AO7 to the metastable PC-MnOx-PMS complex, which was responsible for AO7 oxidation. The PC-MnOx-PMS system also showed substrate preferences based on their redox potentials. Moreover, PC-MnOx could activate periodate (PI) but not peroxydisulfate (PDS) or H2O2. Overall, this study provides a new catalyst for PMS activation through a mild and green synthesis approach.

Catalytic performance and periodate activation mechanism of anaerobic sewage sludge-derived biochar

Periodate (PI)-based advanced oxidation processes are a newly discovered approach for effective pollutant elimination. In this study, we demonstrated that biochar obtained from pyrolysis of anaerobic sewage sludge without any pretreatment can be used for PI activation. The biochar obtained at 800 °C (SBC-800) exhibited the best PI activation capacity using acid organic II (AO7) as substrate. The PI activation was strongly dependent on pH and exhibited the highest AO7 removal rate at pH 3.0. Meanwhile, the anti-interference capacity with common wastewater components and reusability of the SBC-800/PI system were confirmed. Combined with the results of chemical quenching, reactive oxygen species (ROS) trapping, X-ray photoelectric spectroscopy (XPS), electrochemical and density function theory (DFT)-based calculations, singlet oxygen production and electron transfer mediated by the SBC-800-PI complex were the dominant AO7 oxidation mechanisms. This study provides easily prepared catalysts for PI activation and paves the way for solid waste recycling and reuse.

3D Self-Supported Nitrogen-Doped Carbon Nanofiber Electrodes Incorporated Co/CoOx Nanoparticles: Application to Dyes Degradation by Electro-Fenton-Based Process.

We developed free-standing nitrogen-doped carbon nanofiber (CNF) electrodes incorporating Co/CoOx nanoparticles (NPs) as a new cathode material for removing Acid Orange 7 (AO7; a dye for wool) from wastewater by the heterogeneous electro-Fenton reaction. We produced the free-standing N-doped CNF electrodes by electrospinning a polyacrylonitrile (PAN) and cobalt acetate solution followed by thermal carbonation of the cobalt acetate/PAN nanofibers under a nitrogen atmosphere. We then investigated electro-Fenton-based removal of AO7 from wastewater with the free-standing N-doped-CNFs-Co/CoOx electrodes, in the presence or not of Fe2+ ions as a co-catalyst. The electrochemical analysis showed the high stability of the prepared N-doped-CNF-Co/CoOx electrodes in electrochemical oxidation experiments with excellent degradation of AO7 (20 mM) at acidic to near neutral pH values (3 and 6). Electro-Fenton oxidation at 10 mA/cm2 direct current for 40 min using the N-doped-CNF-Co/CoOx electrodes loaded with 25 wt% of Co/CoOx NPs led to complete AO7 solution decolorization with total organic carbon (TOC) removal values of 92.4% at pH 3 and 93.3% at pH 6. The newly developed N-doped-CNF-Co/CoOx electrodes are an effective alternative technique for wastewater pre-treatment before the biological treatment.

Sun-light driven photo degradation of organic dyes from wastewater on precipitation Ag2CrO4 over SiO2-aerogel and nano silica

In this study, Ag2CrO4/SiO2 nanostructure was synthesized by the precipitation method to ameliorate the low specific surface area of Ag2CrO4 with nano-Silica (NS) and Silica Aerogel (SA). The coupled nanophotocatalysts with various weighted contents of Ag2CrO4 and Nano Silica were characterized with PXRD, FESEM, UV–Vis, FTIR and BET-BJH analyses. In order to find the optimal amount, different percentages of Nano Silica 10%, 20% and 30% were investigated. It was observed from BET-BJH that adding Nano Silica lead to an increase the catalyst surface area and crystallinity of synthesis samples. Then, in order to investigate the impact of specific surface area on optimal catalyst activity (Ag2CrO4/Nano Silica (20%)), Silica Aerogel, which has a higher surface area than Nano silica, was used instead of Nano silica. It was observed that increasing the surface area has a direct effect on the activity of the Ag2CrO4. The photocatalytic activity of various nanocomposites was evaluated in the remediation of the organic dyes after 120 min visible light irradiation. The tremendous enhanced photocatalytic activity under the simulated solar light with 95.4% removal of AO7 was observed over Ag2CrO4/Nano Silica (20%) sample. In addition, to illustrate how the influence of various parameters such as various organic dyes, pH, catalyst loading and reusability on the photodegradation efficiency, were conducted over Ag2CrO4/Nano Silica (20). The high activity was obtained in the medium with pH = 7, catalyst loading = 1 g/L and AO7 concentration = 20 mg/L.

Effects of ferroferric oxide on azo dye degradation in a sulfate-containing anaerobic reactor: From electron transfer capacity and microbial community

Anaerobic decolorization of azo dye in sulfate-containing wastewater has been regarded as an economical and effective method, but it is generally limited by the high concentration of azo dye and accumulation of toxic intermediates. To address this problem, Fe3O4 was added to one of the anaerobic reactors to investigate the effects on system performances. Results showed that AO7 removal rate, COD removal rate, and sulfate reduction were enhanced with the addition of Fe3O4 under various influent AO7 concentrations (153 mgCOD/L – 1787 mgCOD/L). According to the proposed pathway for the degradation of AO7, more intermediates (2-hydroxy-1,4-naphthoquinone, phthalide, 4-methylphenol) were produced in the presence of Fe3O4. The electron transfer capacity of sludge was also increased since Fe3O4 could stimulate to secrete humic acid-like organics in EPS. Microbial analysis showed that iron-reducing bacteria like Clostridium and Geobacter were also enriched, which were capable of azo dye and aromatic compounds degradation.

Enhanced removal of acid orange II from aqueous solution by V and N co-doping TiO2-MWCNTs/γ-Al2O3 composite photocatalyst induced by pulsed discharge plasma.

This paper presents a study of V and N co-doping TiO2 embedding multi-walled carbon nanotubes (MWCNTs) supported on γ-Al2O3 pellet (V/N-TiO2-MWCNTs/γ-Al2O3) composite photocatalyst induced by pulsed discharge plasma to enhance the removal of acid orange II (AO7) from aqueous solution. The photocatalytic activity of the V/N-TiO2-MWCNTs/γ-Al2O3 composite to AO7 removal induced by the pulsed discharge plasma was evaluated. The results indicate that the V/N-TiO2-MWCNTs/γ-Al2O3 composite possesses enhanced photocatalytic activity that facilitates the removal of AO7 compared with the TiO2-MWCNTs/γ-Al2O3 and TiO2/γ-Al2O3 composites. Almost 100% of AO7 is removed after 10 min under optimal conditions. The V0.10/N0.05-TiO2-MWCNTs/γ-Al2O3 photocatalyst exhibits the best removal effect for AO7. Analysis of the removal mechanism indicates that the enhancement of the removal of AO7 resulting from V and N co-doping causes TiO2 lattice distortion and introduces a new impurity energy level, which not only reduces the band gap of TiO2 but also inhibits the recombination of the ecb-/hvb+ pairs.

High-efficiency degradation of organic pollutants with Fe, N co-doped biochar catalysts via persulfate activation

In this study, the Fe, N co-doped biochar (Fe-N-BC) was prepared by pyrolyzing wheat straw, urea and iron salts and used to activate persulfate (peroxydisulfate, PS) for organic contaminant degradation. Iron oxide doping not only introduced magnetism into the biochar for easy separation, but also influenced its catalytic ability for PS activation. In the Fe-N-BC/PS system, almost all acid orange (AO7) was removed within 90 min with an apparent rate constant (kobs) of 0.114 min−1, which was almost 37 times larger than that of pure N-BC (0.003 min−1). Factors influencing the removal of AO7 were investigated, including PS concentration, catalyst dosage, and initial pH. The Fe-N-BC/PS system had high removal efficiencies for various organic contaminants and showed high resistance to inorganic anions in aquatic environments. The radical quenching studies, electron paramagnetic resonance (EPR) measurements, and electrochemical analyses verified that the mechanism of AO7 degradation in the Fe-N-BC/PS system included both radical and non-radical pathways involving the generation of OH, SO4−, O2−, 1O2, and electron transfer. Additionally, persistent free radicals (PFRs) on the catalysts also related to their catalytic efficiencies. These results demonstrated that the Fe-N-BC/PS system had the potential for wastewater treatment applications.

One-step preparation of ZVI-sludge derived biochar without external source of iron and its application on persulfate activation

Zero Valent Iron (ZVI) is an important and widely employed environmental remediation material in brownfield. However, the instability of fine size ZVI and the strong aggregation of nanoscale-ZVI limited its further application. To overcome these drawbacks, ZVI-Sludge Derived Biochar (SDBC) was prepared without external iron source through the one-step process of pyrolysis. The characterization results including SEM-EDX, XRD and XPS confirmed the successful loading of Fe0 on the surface of SDBC. The activation efficiency of persulfate (PS) in in-situ chemical oxidation system was studied. The environmental remediation properties of ZVI-SDBC/PS system were evaluated employing acid orange (AO7) and landfill leachate as target pollutants. ZVI-SDBC/PS system was highly efficient as that 99.0% of AO7 (0.06 mM) was removed by 0.925 mM of PS and 0.5 g L−1 of ZVI-SDBC. In addition, total organic carbon (TOC) and ammonia in leachate were removed by 62.8% and 99.8%, respectively. The removal efficiency of AO7 was nearly independent on initial pH as that 89.1% and 99.1% of AO7 were removed at pH of 9.08 and 2.13 respectively. Hydroxyl radicals dominated in the reaction under neutral and alkaline conditions with contribution rates of 71.9% and 86.1% respectively. Noticeably, not only free radicals but also non-radical species such as singlet oxygen contributed to the degradation, which favored the pH-independent performance. The reuse performance of ZVI-SDBC was higher than these of previously reported ZVI-based catalysts as that the first-order rate constant of AO7 removal decreased not much from 0.0718 to 0.0502 min−1 after the three-cycle reuse assays. In summary, ZVI-SDBC showed advantages such as the facile and chemical-saving preparation method, reliable disposal of municipal sewage sludge, remarkable efficiency and stability. These advantages proved ZVI-SDBC/PS system as an effective strategy of controlling waste by waste, and implicated its potential application in full-scale for environmental remediation in brownfield.

Enhanced visible light photocatalytic degradation of dyes in aqueous solution activated by HKUST-1: performance and mechanism

HKUST-1 is a copper-based metal–organic framework (MOF) and potential photocatalyst, but minimal research has addressed the performance and mechanism of HKUST-1 in the visible light photocatalytic degradation of dyes. In the present work, HKUST-1 was applied as a photocatalyst to activate peroxomonosulfate (PMS) under visible light (Vis) for dye removal in aqueous solution. The results showed that the removal efficiency of two cationic dyes [rhodamine B (RhB) and methylene blue (MB)] was greater than 95% within 120 min. Free radicals such as SO4−˙, ·OH were present in the degradation process, with SO4−˙ playing a dominant role. Zeta potential, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy data were used to investigate the degradation mechanism. In the degradation process, surface charge attraction between HKUST-1 and cationic dyes promotes removal efficiency, with the degradation efficiency of cationic dyes (MB and RhB) more than 50% higher than for anionic dyes [acid orange 7 (AO7) and methyl red (MR)]. On the other hand, HKUST-1 has been proved to activate PMS by conducting photoelectrons, which accelerated the degradation of dyes. Compared with the reaction conditions of PMS/Vis, when the HKUST-1 was present (HKUST-1/PMS/Vis), the degradation rates of MB and RhB increased by 62.7 and 63.2%, respectively.