2D Graphene oxide (GO) doped p-n type BiOI/Bi2WO6 as a novel composite for photodegradation of bisphenol A (BPA) in aqueous solutions under UV-vis irradiation

Graphene-based photocatalysts for degradation of organic pollution

Compared with the traditional wastewater treatment technology, semiconductor photocatalysis is a rapidly emerging environment-friendly and efficient Advanced Oxidation Process for degradation of refractory organic contaminants. Single-component semiconductor photocatalysts exhibit poor photocatalytic performance and cannot meet the requirements of wastewater treatment. The combination of semiconductor photocatalysts and Graphene can effectively improve the photocatalytic activity and stability of semiconductor photocatalysts. This review focuses on the synergistic effect of several types of semiconductors with Graphene for photocatalytic degradation of organic pollutants. After a brief introduction of the photodegradation mechanism of semiconductor materials and the basic description of Graphene, the synthesis, characterization and degradation performance of various Graphene-based semiconductor photocatalysts are emphatically introduced.

Antimicrobial potential and rhodamine B dye degradation using graphitic carbon nitride and polyvinylpyrrolidone doped bismuth tungstate supported with in silico molecular docking studies

The environmental-friendly hydrothermal method has been carried out to synthesize Bi2WO6 and g-C3N4/PVP doped Bi2WO6 nanorods (NRs) by incorporating different concentrations of graphitic carbon nitride (g-C3N4) as well as a specified quantity of polyvinylpyrrolidone (PVP). Bi2WO6 doped with g-C3N4 provides structural and chemical stability, reduces charge carriers, degrades dyes, and, owing to lower bandgap energy, is effective for antibacterial, catalytic activity, and molecular docking analysis. The purpose of this research is the treatment of polluted water and to investigate the bactericidal behavior of a ternary system. The catalytic degradation was performed to remove the harmful rhodamine B (RhB) dye using NaBH4 in conjunction with prepared NRs. The specimen compound demonstrated antibacterial activity against Escherichia coli (E. coli) at both high and low concentrations. Higher doped specimens of g-C3N4/PVP-doped Bi2WO6 exhibited a significant improvement in efficient bactericidal potential against E. coli (4.55 mm inhibition zone). In silico experiments were carried out on enoyl-[acylcarrier-protein] reductase (FabI) and β-lactamase enzyme for E. coli to assess the potential of Bi2WO6, PVP doped Bi2WO6, and g-C3N4/PVP-doped Bi2WO6 NRs as their inhibitors and to justify their possible mechanism of action.

Novel synthesis of siligraphene/tungstates (g-SiC/AWO) with promoted transportation of photogenerated charge carriers via direct Z-scheme heterojunctions

We developed here the efficient photocatalysts for the removal of high concentrations of tetracycline under visible light by immobilizing the AWO (A = Ag, Bi, Na) nanocrystals on the surface of siligraphene (g-SiC) nanosheets. The g-SiC/AWO composites was synthesized by magnesiothermic synthesis of g-SiC and sonochemical immobilization of tungstates. These new heterojunctions of g-SiC/tungstates show superior photocatalytic activities in the degradation of high concentrations of tetracycline and 97, 98, and 94% of tetracycline were removed by using low amounts of g-SiC/Ag₂WO₄, g-SiC/Bi₂WO₆, and g-SiC/Na₂WO₄ catalysts, respectively. Based on band structures, the band gaps reduce and the photocatalytic activities were extremely enhanced due to the shortening of electron transfer distance through the Z-scheme mechanism. Also, the graphenic structure of g-SiC is another parameter that was effective in improving photocatalytic performance by increasing the electron transfer and decreasing the rate of electron-hole recombination. Furthermore, the π back-bonding of g-SiC with metal atoms increases the electron-hole separation to enhance the photocatalytic activity. Interestingly, g-SiC composites (g-SiC/AWO) showed much higher photocatalytic properties compared to graphene composites (gr/AWO) and can remove the tetracycline even at dark by producing the oxygenated radicals via adsorption of oxygen on the positive charge of Si atoms in siligraphene structure.

Enhancing Visible Light Photocatalytic Degradation of Bisphenol A Using BiOI/Bi2MoO6 Heterostructures

With the growing population, access to clean water is one of the 21st-century world's challenges. For this reason, different strategies to reduce pollutants in water using renewable energy sources should be exploited. Photocatalysts with extended visible light harvesting are an interesting route to degrade harmful molecules utilized in plastics, as is the case of Bisphenol A (BPA). This work uses a microwave-assisted route for the synthesis of two photocatalysts (BiOI and Bi₂MoO₆). Then, BiOI/Bi₂MoO₆ heterostructures of varied ratios were produced using the same synthetic routes. The BiOI/Bi₂MoO₆ with a flower-like shape exhibited high photocatalytic activity for BPA degradation compared to the individual BiOI and Bi₂MoO₆. The high photocatalytic activity was attributed to the matching electronic band structures and the interfacial contact between BiOI and Bi₂MoO₆, which could enhance the separation of photo-generated charges. Electrochemical, optical, structural, and chemical characterization demonstrated that it forms a BiOI/Bi₂MoO₆ p-n heterojunction. The free radical scavenging studies showed that superoxide radicals (O₂•^-) and holes (h⁺) were the main reactive species, while hydroxyl radical (•OH) generation was negligible during the photocatalytic degradation of BPA. The results can potentiate the application of the microwave synthesis of photocatalytic materials.

Advances in Bi2WO6-Based Photocatalysts for Degradation of Organic Pollutants

With the rapid development of modern industries, water pollution has become an urgent problem that endangers the health of human and wild animals. The photocatalysis technique is considered an environmentally friendly strategy for removing organic pollutants in wastewater. As an important member of Bi-series semiconductors, Bi₂WO₆ is widely used for fabricating high-performance photocatalysts. In this review, the recent advances of Bi₂WO₆-based photocatalysts are summarized. First, the controllable synthesis, surface modification and heteroatom doping of Bi₂WO₆ are introduced. In the respect of Bi₂WO₆-based composites, existing Bi₂WO₆-containing binary composites are classified into six types, including Bi₂WO₆/carbon or MOF composite, Bi₂WO₆/g-C₃N₄ composite, Bi₂WO₆/metal oxides composite, Bi₂WO₆/metal sulfides composite, Bi₂WO₆/Bi-series composite, and Bi₂WO₆/metal tungstates composite. Bi₂WO₆-based ternary composites are classified into four types, including Bi₂WO₆/g-C₃N₄/X, Bi₂WO₆/carbon/X, Bi₂WO₆/Au or Ag-based materials/X, and Bi₂WO₆/Bi-series semiconductors/X. The design, microstructure, and photocatalytic performance of Bi₂WO₆-based binary and ternary composites are highlighted. Finally, aimed at the existing problems in Bi₂WO₆-based photocatalysts, some solutions and promising research trends are proposed that would provide theoretical and practical guidelines for developing high-performance Bi₂WO₆-based photocatalysts.

Development of Efficient Photocatalyst MIL-68(Ga)_NH2 Metal-Organic Framework for the Removal of Cr(VI) and Cr(VI)/RhB from Wastewater under Visible Light

Severe environmental pollution is caused by the massive discharge of complex industrial wastewater. The photocatalytic technology has been proved as an effective way to solve the problem, while an efficient photocatalyst is the most critical factor. Herein, a new photocatalyst MIL-68(Ga)_NH₂ was obtained by hydrothermal synthesis and were characterized by PXRD, FTIR, ¹H NMR, and TGA systematically. The result demonstrates that MIL-68(Ga)_NH₂ crystallized in orthorhombic system and Cmcm space group with the unit cell parameters: a = 36.699 Å, b = 21.223 Å, c = 6.75 Å, V = 5257.6 ų, which sheds light on the maintenance of the crystal structure of the prototype material after amino modification. The conversion of Cr(VI) and binary pollutant Cr(VI)/RhB in wastewater under visible light stimulation was characterized by the UV-vis DRS. Complementary experimental results indicate that MIL-68(Ga)_NH₂ exhibits remarkable photocatalytic activity for Cr(VI) and the degradation rate reaches as high as 98.5% when pH = 2 and ethanol as hole-trapping agent under visible light irradiation with good reusability and stability. Owing to the synergistic effect between Cr(VI) and RhB in the binary pollutant system, MIL-68(Ga)_NH₂ exhibits excellent catalytic activity for both the pollutants, the degradation efficiency of Cr(VI) and RhB was up to 95.7% and 94.6% under visible light irradiation for 120 min, respectively. The possible removal mechanism of Cr(VI)/RhB based on MIL-68(Ga)_NH₂ was explored. In addition, Ga-based MOF was applied in the field of photocatalytic treatment of wastewater for the first time, which broadened the application of MOF materials in the field of photocatalysis.

Transformation of Solid Waste Management in China: Moving towards Sustainability through Digitalization-Based Circular Economy

In China, environmental pollution due to municipal solid waste (MSW) over-generation is one of the country’s priority concerns. The increasing volume and complexity of the waste poses serious risks to the environment and public health. Currently, the annual growth of MSW generation is estimated to be approximately 8–10% and will increase to 323 million metric tons (Mt) by 2030. Based on the secondary data collected from a literature survey, this article critically evaluates the recent progress of MSW management (MSWM) in China and offers new insights into the waste sector in the era of Industry 4.0. This helps decision makers in China to plan a smooth transition nationwide to a circular economy (CE) in the waste sector. It is evident that digitalization is a driving force for China to move towards low-carbon development strategies within the framework of CE. Through digitalization, the waste sector has promoted prevention, reduction, reuse, and recycling (3Rs) of waste before waste disposal in landfills. A proper implementation of digitalization-based waste recycling has contributed to an efficient cooperation between the government and private sector, increased job opportunities, and promoted the conservation of resources. It is anticipated that this work not only contributes to the establishment of an integrated MSWM system in China, but also improves local MSWM through digitalization in the framework of a CE.

Synthesis of bismuth oxyhalide (BiOBrzI(1-z)) solid solutions for photodegradation of methylene blue dye

Background: The removal of textile wastes is a priority due to their mutagenic and carcinogenic properties.  In this study, bismuth oxyhalide was used in the removal of methylene blue (MB) which is a textile waste. The main objective of this study was to develop and investigate the applicability of a bismuth oxyhalide (BiOBr _zI _(1-z)) solid solutions in the photodegradation of MB under solar and ultraviolet (UV) light irradiation.

Methods: Bismuth oxyhalide (BiOBr _zI _(1-z)) (0 ≤ z ≤ 1) materials were successfully prepared through the hydrothermal method. Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM), X-ray diffractometer (XRD), and scanning electron microscope (SEM) were used to determine the surface area, microstructure, crystal structure, and morphology of the resultant products. The photocatalytic performance of BiOBr _zI _(1-z) materials was examined through methylene blue (MB) degradation under UV light and solar irradiation.

Results: The XRD showed that BiOBr _zI _(1-z) materials crystallized into a tetragonal crystal structure with (102) peak slightly shifting to lower diffraction angle with an increase in the amount of iodide (I ^-). BiOBr _0.6I _0.4 materials showed a point of zero charge of 5.29 and presented the highest photocatalytic activity in the removal of MB with 99% and 88% efficiency under solar and UV irradiation, respectively. The kinetics studies of MB removal by BiOBr _zI _(1-z) materials showed that the degradation process followed nonlinear pseudo-first-order model indicating that the removal of MB depends on the population of the adsorption sites. Trapping experiments confirmed that photogenerated holes (h ⁺) and superoxide radicals ( ^•O ₂⁻) are the key species responsible for the degradation of MB.

Conclusions: This study shows that bismuth oxyhalide materials are very active in the degradation of methylene blue dye using sunlight and thus they have great potential in safeguarding public health and the environment from the dye’s degradation standpoint. Moreover, the experimental results agree with nonlinear fitting.

Removal of emerging contaminants (bisphenol A and antibiotics) from kitchen wastewater by alkali-modified biochar

Using current wastewater treatment technologies, it can be challenging to remove the emerging contaminants (ECs) present in kitchen wastewater (KW) of complex compositions and high organic content. In this study, biochar, derived from straw, was modified as an adsorbent to remove ECs such as bisphenol A (BPA), tetracycline (TC) and ofloxacin (OFL) from a complex KW system. An alkali-modified biochar, having larger specific surface areas and stronger hydrophobicity, was found to exhibit a higher adsorption capacity, with more than 95% of the target ECs being removed. Indeed, in a static operation mode, the alkali-modified biochar had maximum adsorption capacities of 71.43, 101.01 and 54.05 mg/g for BPA, TC, and OFL, respectively. The adsorption kinetics and isotherms models indicated that the adsorption process was controlled by chemisorption, as well as the monolayer adsorption of contaminants onto the external and internal surfaces of the alkali-modified biochar. The adsorption of TC and OFL was significantly affected by the initial pH values of KW. However, the presence of different environmental factors (COD, NH₄⁺ and PO₄^3-) had little effects on the adsorption of the contaminants. The alkali-modified biochar was further tested in a fixed-bed column where the maximum dynamic adsorption capacities for BPA and OFL were 55 and 45 mg/g, representing about 75% and 83% of the static saturated adsorption capacities. These findings can be of major significance for the application of alkali-modified biochar in the removal of ECs from complex KW systems.

Synthesis of an organic phosphoric acid-based multilayered SERS imprinted sensor for selective detection of dichlorophenol

A novel SERS imprinted sensor (AIM@MIPs) was prepared, which could improve the detection ability of analysis detection. The AIM@MIPs presented sensitive and selective detection property to 2,6-DCP.

Harnessing landfill gas (LFG) for electricity: A strategy to mitigate greenhouse gas (GHG) emissions in Jakarta (Indonesia)

Due to its increasing demands for fossil fuels, Indonesia needs an alternative energy to diversify its energy supply. Landfill gas (LFG), which key component is methane (CH₄), has become one of the most attractive options to sustain its continued economic development. This exploratory study seeks to demonstrate the added value of landfilled municipal solid waste (MSW) in generating sustainable energy, resulting from CH₄ emissions in the Bantargebang landfill (Jakarta). The power generation capacity of a waste-to-energy (WTE) plant based on a mathematical modeling was investigated. This article critically evaluated the production of electricity and potential income from its sale in the market. The project's environmental impact assessment and its socio-economic and environmental benefits in terms of quantitative and qualitative aspects were discussed. It was found that the emitted CH₄ from the landfill could be reduced by 25,000 Mt annually, while its electricity generation could reach one million kW ⋅h annually, savings on equivalent electricity charge worth US$ 112 million/year (based on US' 8/kW ⋅ h). An equivalent CO₂ mitigation of 3.4 × 10⁶ Mt/year was obtained. The income from its power sale were US$ 1.2 ×10⁶ in the 1^st year and 7.7 ×10⁷US$ in the 15^th year, respectively, based on the projected CH₄ and power generation. The modeling study on the Bantargebang landfill using the LFG extraction data indicated that the LFG production ranged from 0.05 to 0.40 m³ per kg of the landfilled MSW. The LFG could generate electricity as low as US' 8 per kW ⋅ h. With respect to the implications of this study, the revenue not only defrays the cost of landfill's operations and maintenance (O&M), but also provides an incentive and means to further improve its design and operations. Overall, this work not only leads to a diversification of primary energy, but also improves environmental protection and the living standard of the people surrounding the plant.

Synthesis of bismuth oxyhalide (BiOBr zI (1- z)) solid solutions for photodegradation of methylene dye

Background: The removal of textile wastes is a priority due to their mutagenic and carcinogenic properties.  In this study, bismuth oxyhalide was used in the removal of methylene blue (MB) which is a textile waste. The main objective of this study was to develop and investigate the applicability of a bismuth oxyhalide (BiOBr _zI _(1-z)) solid solutions in the photodegradation of MB under solar and ultraviolet (UV) light irradiation. Methods: Bismuth oxyhalide (BiOBr _zI _(1-z)) (0 ≤ z ≤ 1) materials were successfully prepared through the hydrothermal method. Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM), X-ray diffractometer (XRD), and scanning electron microscope (SEM) were used to determine the surface area, microstructure, crystal structure, and morphology of the resultant products. The photocatalytic performance of BiOBr _zI _(1-z) materials was examined through methylene blue (MB) degradation under UV light and solar irradiation. Results: The XRD showed that BiOBr _zI _(1-z) materials crystallized into a tetragonal crystal structure with (102) peak slightly shifting to lower diffraction angle with an increase in the amount of iodide (I ^-). BiOBr _0.6I _0.4 materials showed a point of zero charge of 5.29 and presented the highest photocatalytic activity in the removal of MB with 99% and 88% efficiency under solar and UV irradiation, respectively. The kinetics studies of MB removal by BiOBr _zI _(1-z) materials showed that the degradation process followed nonlinear pseudo-first-order model indicating that the removal of MB depends on the population of the adsorption sites. Trapping experiments confirmed that photogenerated holes (h ⁺) and superoxide radicals ( ^•O ₂ ^-) are the key species responsible for the degradation of MB. Conclusions : This study shows that bismuth oxyhalide materials are very active in the degradation of methylene blue dye using sunlight and thus they have great potential in safeguarding public health and the environment from the dye's degradation standpoint. Moreover, the experimental results agree with nonlinear fitting.

Oxygen vacancy BiO2-x/Bi2WO6 synchronous coupling with Bi metal for phenol removal via visible and near-infrared light irradiation

The introduction of oxygen-defects has been a versatile strategy to enhance photocatalysis efficiency. In this work, a 2D/3D Bi/BiO_2-x/Bi₂WO₆ heterojunction photocatalyst with rich oxygen-defective was in sequence prepared through a facile solvothermal method, which displays favorable photocatalytic activity towards organic contaminants under visible-NIR light irradiation. The enhancement in photocatalytic performance can be attributed to the synergistic effect between oxygen-vacancy-rich heterojunction and the localized surface plasmon resonance induced by metallic Bi. The functional group interaction, surface morphology, crystal structure, element composition, and tuned bandgap were investigated by FT-IR, SEM, Raman shift, ICP-MS, and XPS technique. The spectrum response performance of the photocatalyst was verified by UV-visible DRS analysis. Results of photodegradation experiments toward organic contaminants showed that the prepared photocatalyst can degrade 90% of phenol in 20 mins under visible-NIR light irradiation, both Z-scheme heterojunction and the introduction of Bi metal contribute to the enhancement in the photocatalytic activity. The results of the DFT calculation suggest that the valence band-edge hybridization within BiO_2-x and Bi₂WO₆ can effectively enhance the photocatalytic performance by increasing the migration efficiencies of electron-hole pairs. Moreover, a possible mechanism was proposed on the results of EIS, ESR and GC-MS tests. This work offers a novel insight for synthesizing efficient visible-NIR light photocatalysis by activating the semiconductors with Bi metal.

Resource recovery from landfill leachate: An experimental investigation and perspectives

This work investigates the performances of coconut shell waste-based activated carbon (CSWAC) adsorption in batch studies for removal of ammoniacal nitrogen (NH₃-N) and refractory pollutants (as indicated by decreasing COD concentration) from landfill leachate. To valorize unused resources, coconut shell, recovered and recycled from agricultural waste, was converted into activated carbon, which can be used for leachate treatment. The ozonation of the CSWAC was conducted to enhance its removal performance for target pollutants. The adsorption mechanisms of refractory pollutants by the adsorbent are proposed. Perspectives on nutrient recovery technologies from landfill leachate from the view-points of downstream processing are presented. Their removal efficiencies for both recalcitrant compounds and ammoniacal nitrogen were compared to those of other techniques reported in previous work. It is found that the ozonated CSWAC substantially removed COD (i.e. 76%) as well as NH₃-N (i.e. 75%), as compared to the CSWAC without pretreatment (i.e. COD: 44%; NH₃-N: 51%) with NH₃-N and COD concentrations of 2750 and 8500 mg/L, respectively. This reveals the need of ozonation for the adsorbent to improve its performance for the removal of COD and NH₃-N at optimized reactions: 30 g/L of CSWAC, pH 8, 200 rpm of shaking speed and 20 min of reaction time. Nevertheless, treatment of the leachate samples using the ozonated CSWAC alone was still unable to result in treated effluents that could meet the COD and NH₃-N discharge standards below 200 and 5 mg/L, respectively, set by legislative requirements. This reveals that another treatment is necessary to be undertaken to comply with the requirement of their effluent limit.

Resource recovery toward sustainability through nutrient removal from landfill leachate

This study investigated the feasibility of integrated ammonium stripping and/or coconut shell waste-based activated carbon (CSWAC) adsorption in treating leachate samples. To valorize unused biomass for water treatment application, the adsorbent originated from coconut shell waste. To enhance its performance for target pollutants, the adsorbent was pretreated with ozone and NaOH. The effects of pH, temperature, and airflow rate on the removal of ammoniacal nitrogen (NH₃-N) and refractory pollutants were studied during stripping alone. The removal performances of refractory compounds in this study were compared to those of other treatments previously reported. To contribute new knowledge to the field of study, perspectives on nutrients removal and recovery like phosphorus and nitrogen are presented. It was found that the ammonium stripping and adsorption treatment using the ozonated CSWAC attained an almost complete removal (99%) of NH₃-N and 90% of COD with initial NH₃-N and COD concentrations of 2500 mg/L and 20,000 mg/L, respectively, at optimized conditions. With the COD of treated effluents higher than 200 mg/L, the combined treatments were not satisfactory enough to remove target refractory compounds. Therefore, further biological processes are required to complete their biodegradation to meet the effluent limit set by environmental legislation. As this work has contributed to resource recovery as the driving force of landfill management, it is important to note the investment and operational expenses, engineering applicability of the technologies, and their environmental concerns and benefits. If properly managed, nutrient recovery from waste streams offers environmental and socio-economic benefits that would improve public health and create jobs for the local community.

Arsenic removal in aqueous solutions using FeS2

This study tested the technical feasibility of pyrite and/or persulfate oxidation system for arsenic (As) removal from aqueous solutions. The effects of persulfate on As removal by the pyrite in the integrated treatment were also investigated. Prior to the persulfate addition into the reaction system, the physico-chemical interactions between As and the pyrite alone in aqueous solutions were explored in batch studies. The adsorption mechanisms of As by the adsorbent were also presented. At the same As concentration of 5 mg/L, it was found that As(III) attained a longer equilibrium time (8 h) than As(V) (2 h), while the pyrite worked effectively at pH ranging from 6 to 11. At optimum conditions (0.25 g/L of pyrite, pH 8.0 and 5 mg/L of As(III) concentration), the addition of persulfate (0.5 mM) into the reaction promoted a complete removal of arsenic from the solutions. Consequently, this enabled the treated effluents to meet the arsenic maximum contaminant limit (MCL) of <10 μg/L according to the World Health Organization (WHO)'s requirements. The redox mechanisms, which involved electron transfer from the S₂^2- of the pyrite to Fe³⁺, supply Fe²⁺ for persulfate decomposition, oxidizing As(III) to As(V). The sulfur species played roles in the redox cycle of the Fe³⁺/Fe²⁺ of the pyrite by giving its electrons, while the As(III) oxidation to As(V) was attributed to the pyrite. Overall, this work reveals the applicability of the pyrite as an adsorbent for water treatment and the importance of persulfate addition to promote a complete As removal from aqueous solutions.

Recovering heavy metals from electroplating wastewater and their conversion into Zn2Cr-layered double hydroxide (LDH) for pyrophosphate removal from industrial wastewater

This work incorporated technological values into Zn₂Cr-layered double hydroxide (LDH), synthesized from unused resources, for removal of pyrophosphate (PP) in electroplating wastewater. To adopt a resource recovery for the remediation of the aquatic environment, the Zn₂Cr-LDH was fabricated by co-precipitation from concentrated metals of plating waste that remained as industrial by-products from metal finishing processes. To examine its applicability for water treatment, batch experiments were conducted at optimum M²⁺/M³⁺, pH, reaction time, and temperature. To understand the adsorption mechanisms of the PP by the adsorbent, the Zn₂Cr-LDH was characterized using Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses before and after adsorption treatment. An almost complete PP removal was attained by the Zn₂Cr-LDH at optimized conditions: 50 mg/L of PP, 1 g/L of adsorbent, pH 6, and 6 h of reaction. Ion exchange controlled the PP removal by the adsorbent at acidic conditions. The PP removal well fitted a pseudo-second-order kinetics and/or the Langmuir isotherm model with 79 mg/g of PP adsorption capacity. The spent Zn₂Cr-LDH was regenerated with NaOH with 86% of efficiency for the first cycle. The treated effluents could comply with the discharge limit of <1 mg/L. Overall, the use of the Zn₂Cr-LDH as a low-cost adsorbent for wastewater treatment has contributed to national policy that promotes a zero-waste approach for a circular economy (CE) through a resource recovery paradigm.

Highly efficient activation of peroxymonosulfate by Co3O4/Bi2WO6 p-n heterojunction composites for the degradation of ciprofloxacin under visible light irradiation

Photocatalytic technology assisted via peroxymonosulfate (PMS) has good potential in water treatment. In this study, the Co₃O₄/Bi₂WO₆ composite was constructed via an in-situ calcination process and used to activate PMS for the degradation of ciprofloxacin (CIP) under visible light irradiation. The obtained 5 wt% Co₃O₄/Bi₂WO₆(CBWO-2) can highly effectively remove 86.2% CIP within 5 min visible light irradiation in presence of PMS. The excellent degradation performance of Co₃O₄/Bi₂WO₆/PMS system can be attributed to the synergistic effect between p-n heterojunction and PMS activation. The conduction band and valence band deviation between Co₃O₄ and Bi₂WO₆ were calculated by XPS techniques. Besides, DFT calculations were performed to further confirm the internal structure between Co₃O₄ and Bi₂WO₆. This work not only provides an approach to fabricate heterostructures but also indicated that Co₃O₄/Bi₂WO₆/PMS/Vis system is a potential environment remediation alternative for the efficient removal of recalcitrant organic compounds from wastewaters.

Functionalizing TiO2 with graphene oxide for enhancing photocatalytic degradation of methylene blue (MB) in contaminated wastewater

Methylene blue is a refractory pollutant commonly present in textile wastewater. This study tests the feasibility of TiO₂/graphene oxide (GO) composite in enhancing photocatalytic degradation of MB in synthetic wastewater with respect to scientific and engineering aspects. To enhance its removal, we vary the composition of the composite based on the TiO₂ weight. Under UV-vis irradiation, the effects of photocatalyst's dose, pH, and reaction time on MB removal by the composites are evaluated under optimum conditions, while any changes in their physico-chemical properties before and after treatment are analyzed by using TEM, SEM, XRD, FTIR and BET. The photodegradation pathways of the target pollutant by the composite and its removal mechanisms are also elaborated. It is found that the same composite with a 1:2 wt ratio of GO/TiO₂ has the largest surface area of 104.51 m²/g. Under optimum reactions (0.2 g/L of dose, pH 10, and 5 mg/L of pollutant's concentration), an almost complete MB removal could be attained within 4 h. This result is higher than that of the TiO₂ alone (30%) under the same conditions. Since the treated effluents could meet the strict discharge standard limit of ≤0.2 μg/L set by China's regulation, subsequent biological treatments are unnecessary for completing biodegradation of remaining oxidation by-products in the wastewater effluents.

Fabrication, characterization, and application of ternary magnetic recyclable Bi2WO6/BiOI@Fe3O4 composite for photodegradation of tetracycline in aqueous solutions

We aim at fabricating a ternary magnetic recyclable Bi₂WO₆/BiOI@Fe₃O₄ composite that could be applied for photodegradation of tetracycline (TC) from synthetic wastewater. To identify any changes with respect to the composite's morphology and crystal structure properties, ΧRD, FTIR, FESEM-EDS, PL and VSM analyses are carried out. The effects of Fe₃O₄ loading ratio on the Bi₂WO₆/BiOI for TC photodegradation are evaluated, while operational parameters such as pH, reaction time, TC concentration, and photocatalyst's dose are optimized. Removal mechanisms of the TC by the composite and its photodegradation pathways are elaborated. With respect to its performance, under the same optimized conditions (1 g/L of dose; 5 mg/L of TC; pH 7; 3 h of reaction time), the Bi₂WO₆/BiOI@5%Fe₃O₄ composite has the highest TC removal (97%), as compared to the Bi₂WO₆ (63%). After being saturated, the spent photocatalyst could be magnetically separated from solution for subsequent use. In spite of three consecutive cycles with 71% of efficiency, the spent composite still has reasonable photocatalytic activities for reuse. Overall, this suggests that the composite is a promising photocatalyst for TC removal from aqueous solutions.

Enhanced photocatalytic degradation of organic pollutants using carbon nanotube mediated CuO and Bi2WO6 sandwich flaky structures

CuO/CNT/Bi2WO6 composites were synthesized with a solvothermal and impregnation-calcination method. This material combines the advantages of CuO, carbon nanotubes (CNTs) and Bi2WO6. The photocatalytic activity of the catalyst was evaluated by degrading phenolic organic pollutants such as p-nitrophenol and phenol under visible light. Compared with pure Bi2WO6, the photocatalytic activity of CuO/CNT/Bi2WO6 composites is significantly increased by a factor of 3.52. The main reason for the increased activity is that the doped CNTs and CuO promote the separation of photogenerated hole and electron pairs. In addition, the coupling of π-π electrons on the CNT surface with the pollutants promotes the adsorption of the pollutants on the photocatalyst surface. The degradation rate of pure photocatalytic degradation of phenol can reach 60%. Under the synergistic effect of H2O2, the degradation rate of phenol can reach 94%, which is 1.56 times higher than that of pure photocatalysis. The UV-vis absorption spectrum shows that CuO/CNT/Bi2WO6 has stronger light absorption ability in both visible and ultraviolet light regions. The trapping experiments of active species show that h + and • OH are the main active substances for photocatalytic degradation of phenol. This paper proposes a Z scheme mechanism to improve the photocatalytic performance.