Surface oxygen vacancies enriched FeOOH/Bi2MoO6 photocatalysis- fenton synergy degradation of organic pollutants

Carbon dots-loaded cellulose nanofibrils hydrogel incorporating Bi2O3/BiOCOOH for effective adsorption and photocatalytic degradation of lignin

A novel photocatalytic adsorbent, a cellulose nanofibrils based hydrogel incorporating carbon dots and Bi2O3/BiOCOOH (designated as CCHBi), was developed to address lignin pollution. CCHBi exhibited an adsorption capacity of 435.0 mg/g, 8.9 times greater than that of commercial activated carbon. This enhanced adsorption performance was attributed to the 3D porous structure constructed using cellulose nanofibrils (CNs), which increased the specific surface area and provided additional sorption sites. Adsorption and photocatalytic experiments showed that CCHBi had a photocatalytic degradation rate constant of 0.0140 min-1, 3.1 times higher than that of Bi2O3/BiOCOOH. The superior photocatalytic performance of CCHBi was due to the Z-scheme photocatalytic system constructed by carbon dots-loaded cellulose nanofibrils and Bi2O3/BiOCOOH, which facilitated the separation of photoinduced charge carriers. Additionally, the stability of CCHBi was confirmed through consecutive cycles of adsorption and photocatalysis, maintaining a removal efficiency of 85 % after ten cycles. The enhanced stability was due to the 3D porous structure constructed by CNs, which safeguarded the Bi2O3/BiOCOOH. This study validates the potential of CCHBi for high-performance lignin removal and promotes the application of CNs in developing new photocatalytic adsorbents.

Oxygen vacancy-rich β-Bi2O3/Bi2O2SiO3 Z-Scheme heterojunction: A strategy to enhance visible light-driven photocatalytic removal of ARB and ARGs

Oxygen vacancy-rich β-Bi2O3/Bi2O2SiO3 (BO/BOS) Z-Scheme heterojunction was prepared by hydrothermal method-assisted calcination. Under visible light, β-Bi2O3/Bi2O2SiO3 photocatalyst demonstrated superior photocatalytic efficacy in degrading antibiotics and antibiotic-resistant Escherichia coli (AR E. coli) compared to individual β-Bi2O3 and Bi2O2SiO3. The experimental results showed that BO/BOS-450 sample possessed the best photocatalytic activity against tetracycline (2 h, 80.8%), amoxicillin (4 h, 57.9%) and AR E. coli (3 h, 107.43 CFU·mL-1). BO/BOS-450 sample showed 91.8% electrostatic capture of AR E. coli in the bacterial capture experiment. In the antibiotic-resistant genes (ARGs) degradation experiment, BO/BOS-450 sample was able to bring the log10 (Ct/C0) value of tetA to -3.49 after 2 h. Oxygen vacancies (OVs) were verified through HR-TEM, XPS and EPR analyses. ESR experiments aligned with the quenching experiment results, confirming that the crucial active species were ‧O2- and h+ during photocatalytic sterilization. A small-scale sewage treatment equipment was designed for the effective removal of ARB from real water samples.

Unravelling the Role of Free Radicals in Photocatalysis

Free radicals are increasingly recognized as active intermediate reactive species that can participate in various redox processes, significantly influencing the mechanistic pathways of reactions. Numerous researchers have investigated the generation of one or more distinct photogenerated radicals, proposing various hypotheses to explain the reaction mechanisms. Notably, recent research has demonstrated the emergence of photogenerated radicals in innovative processes, including organic chemical reactions and the photocatalytic dissolution of precious metals. To harness the potential of these free radicals more effectively, it is imperative to consolidate and analyze the processes and action modes of these photogenerated radicals. This conceptual paper delves into the latest advancements in understanding the mechanics of photogenerated radicals.

Fabrication of nano-hammer shaped CuO@HApNWs for catalytic degradation of tetracycline

With widespread and excessive use of antibiotics in medicine, poultry farming, and aquaculture, antibiotic residues have become a significant threat to both eco-environment and human health. In this paper, using hydroxyapatite nanowires (HApNWs) as an ecologically compatible carrier, a novel nano-hammer shaped conjunction with HApNW conjugating CuO microspheres (CuO@HApNWs) was successfully synthesized by in-situ agglomeration method. The catalytic degradation performance of the nano-hammer shaped CuO@HApNWs with Fenton-like activation was investigated by using tetracycline (TC) as a representative antibiotic pollutant. Remarkably, it exhibited excellent catalytic activity, which the removal rate of TC got to 92.0% within 40 min, and the pseudo-second-order reaction kinetic constant was 18.33 × 10-3 L mg-1·min-1, which was 26 times and 5 times than that of HApNWs and CuO, respectively. Furthermore, after recycling 6 times, the degradation efficiency of TC still remained above 85 %. Based on radical scavenger tests and electron paramagnetic resonance (EPR) spectroscopy, it demonstrated that the excellent activity of CuO@HApNWs was mainly attributed to the fact that Fenton-like activation promotes the circulation of Cu2+ and Cu+, the generated main active oxygen species (•OH and O2-•) achieve efficient degradation of TC. In summary, the nano-hammer shaped CuO@HApNWs could be in-situ synthesed, and used as an eco-friendly Fenton-like catalyst for effectively catalytic degradation of organic pollutants, which has great potential for wastewater treatment.

Broad Spectral Response FeOOH/BiO2-x Photocatalyst with Efficient Charge Transfer for Enhanced Photo-Fenton Synergistic Catalytic Activity

In this work, to promote the separation of photogenerated carriers, prevent the catalyst from photo-corrosion, and improve the photo-Fenton synergistic degradation of organic pollutants, the coating structure of FeOOH/BiO2-x rich in oxygen vacancies was successfully synthesized by a facile and environmentally friendly two-step process of hydrothermal and chemical deposition. Through a series of degradation activity tests of synthesized materials under different conditions, it was found that FeOOH/BiO2-x demonstrated outstanding organic pollutant degradation activity under visible and near-infrared light when hydrogen peroxide was added. After 90 min of reaction under photo-Fenton conditions, the degradation rate of Methylene Blue by FeOOH/BiO2-x was 87.4%, significantly higher than the degradation efficiency under photocatalysis (60.3%) and Fenton (49.0%) conditions. The apparent rate constants of FeOOH/BiO2-x under photo-Fenton conditions were 2.33 times and 3.32 times higher than photocatalysis and Fenton catalysis, respectively. The amorphous FeOOH was tightly coated on the layered BiO2-x, which significantly increased the specific surface area and the number of active sites of the composites, and facilitated the improvement of the separation efficiency of the photogenerated carriers and the prevention of photo-corrosion of BiO2-x. The analysis of the mechanism of photo-Fenton synergistic degradation clarified that ·OH, h+, and ·O2- are the main active substances involved in the degradation of pollutants. The optimal degradation conditions were the addition of the FeOOH/BiO2-x composite catalyst loaded with 20% Fe at a concentration of 0.5 g/L, the addition of hydrogen peroxide at a concentration of 8 mM, and an initial pH of 4. This outstanding catalytic system offers a fresh approach to the creation and processing of iron-based photo-Fenton catalysts by quickly and efficiently degrading various organic contaminants.

Embedding Atomically Dispersed Manganese/Gadolinium Dual Sites in Oxygen Vacancy-Enriched Biodegradable Bimetallic Silicate Nanoplatform for Potentiating Catalytic Therapy

Due to their atomically dispersed active centers, single-atom nanozymes (SAzymes) have unparalleled advantages in cancer catalytic therapy. Here, loaded with chlorin e6 (Ce6), a hydrothermally mass-produced bimetallic silicate-based nanoplatforms with atomically dispersed manganese/gadolinium (Mn/Gd) dual sites and oxygen vacancies (OVs) (PMnSA GMSNs-V@Ce6) is constructed for tumor glutathione (GSH)-triggered chemodynamic therapy (CDT) and O2 -alleviated photodynamic therapy. The band gaps of silica are significantly reduced from 2.78 to 1.88 eV by doping with metal ions, which enables it to be excited by a 650 nm laser to produce electron-hole pairs, thereby facilitating the generation of reactive oxygen species. The Gd sites can modulate the local electrons of the atom-catalyzed Mn sites, which contribute to the generation of superoxide and hydroxyl radicals (• OH). Tumor GSH-triggered Mn2+ release can convert endogenous H2 O2 to • OH and realize GSH-depletion-enhanced CDT. Significantly, the hydrothermally generated OVs can not only capture Mn and Gd atoms to form atomic sites but also can elongate and weaken the O-O bonds of H2 O2 , thereby improving the efficacy of Fenton reactions. The degraded Mn2+ /Gd3+ ions can be used as tumor-specific magnetic resonance imaging contrast agents. All the experimental results demonstrate the great potential of PMnSA GMSNs-V@Ce6 as cancer theranostic agent.

Boosting Photocatalytic Nitrogen Fixation via Nanoarchitectonics Using Oxygen Vacancy Regulation in W-Doped Bi2MoO6 Nanosheets

Ammonia and nitrates are key raw materials for various chemical and pharmaceutical industries. The conventional methods like Haber-Bosch and Ostwald methods used in the synthesis of ammonia and nitrates, respectively, result in harmful emission of gases. In recent years, the photocatalytic fixation of N2 into NH3 and nitrates has become a hot topic since it is a green and cost-effective approach. However, the simultaneous production of ammonia and nitrates has not been studied much. In this regard, we have synthesized W-doped Bi2MoO6 nanosheets in various molar ratios and demonstrated their potential as efficient photocatalysts for the simultaneous production of NH3 and NO3- ions under visible light irradiation. It was found that one of the catalysts (BMWO0.4) having an optimal molar ratio of doped tungsten showed the best photocatalytic NH3 production (56 μmol h-1) without using any sacrificial agents along with the simultaneous production of NO3- ions at a rate of 7 μmol h-1. The enhanced photocatalytic activity of the synthesized photocatalysts could be ascribed to oxygen vacancy defects caused by Mo substitution by a more electronegative W atom. Furthermore, density functional theory calculations verified the alteration in the band gap after doping of W atoms and also showed a strong chemisorption of N2 over the photocatalyst surface leading to its activation and thereby enhancing the photocatalytic activity. Thus, the present work provides insights into the effect of structural distortions on tailoring the efficiency of materials used in photocatalytic N2 fixation.

Enhanced Photocatalytic Degradation of Indoor Low Concentration Gaseous Formaldehyde by Asymmetric Silveriodate Composited with 2D or 3D Bismuth Oxybromide

Formaldehyde is one of the most hazardous and typical indoor VOCs air pollutants. Asymmetric AgIO3 was respectively composited with 3D hierarchically structured BiOBr and 2D BiOBr nanosheets to photodegrade gas-phase formaldehyde. Ag/AgIO3 /BiOBr(CMC) demonstrated better photocatalytic performance than Ag/AgIO3 /BiOBr owning to the role of biomass solvent sodium carboxymethyl cellulose in increasing the specific surface area, reducing the band gap and changing the dominant facets. Moreover, Ag nanoparticles coming from the reduction in AgIO3 were confirmed by XRD, SEM and XPS. The surface plasma resonance effect of Ag NPs improved the efficiency of the light quantum. Besides, different exposed facets of {010} in BiOBr(CMC) and {001} in BiOBr resulted in distinct oxygen vacancy structures.O 2 2 - could be generated via a two-electron transfer pathway on the {010} dominant facets surface in AABR-CMC, leading to the change in photolysis pathway and facilitating more · OH produced by AABR-CMC. Compared with pure AgIO3 and BiOBr or BiOBr(CMC), the photocatalytic efficiency of the composites was improved significantly. Optimal photodegradation efficiency for HCHO was achieved for AABR-75 and AABR-CMC50.

2D defect-engineered Ag-doped γ-Fe2O3/BiVO4: The effect of noble metal doping and oxygen vacancies on exciton-triggering photocatalysis production of singlet oxygen

The selectivity of singlet oxygen (1O2) holds promising applications in complex environmental systems due to its ability to preferentially oxidize target pollutants. Usually, 1O2 in photocatalytic systems is generated via the electron transfer pathway and •O2- plays an important role as an intermediate, while the exciton-based energy transfer pathway for 1O2 generation has been less studied. Here, a 2D Ag-γ-Fe2O3/BiVO4 with oxygen vacancies was designed which was capable of generating 1O2 by an exciton-based energy transfer-dominated approach, as strongly demonstrated by the results of steady-state fluorescence spectroscopy and phosphorescence spectroscopy. In the Z-type heterojunction photocatalyst system, Ag acted as an electron mediator to promote not only the generation of free carriers but also the generation of singlet excitons, while the appropriate concentration of oxygen vacancies further promotes the exciton-triggering photocatalysis production of 1O2. The Ag-γ-Fe2O3/BiVO4 could degrade 99.4% of sulfadiazine within 90 min, and 1O2 played an important role in the degradation of sulfadiazine, as shown by EPR and active species capture experiments. Ecotoxicity predictions indicated that the main byproducts of sulfadiazine degradation by Ag-γ-Fe2O3/BiVO4 were low in toxicity. The prepared photocatalysts provide a new idea for obtaining 1O2 and designing photocatalysts with selectivity.

Synthesis of β-FeOOH/polyaniline heterogeneous catalyst for efficient photo-Fenton degradation of AOII dye

Discharge of the untreated dye-containing wastewaters will induce water source pollution and further harm aquatic organisms. In this study, the akaganéite/polyaniline catalyst (β-FeOOH/PANI, about 1.0 μm) could be successfully composed by polyaniline (PANI, (C₆H₇N)_n, 200-300 nm) and akaganéite (β-FeOOH, FeO(OH)_1-xCl_x, less than 200 nm), according to the identification and characterization results of XRD, Ramon, FTIR, XPS, SEAD, EDS, and FESEM (or HRTEM). Due to PANI providing more photogenerated electrons, the β-FeOOH/PANI composite (compared with β-FeOOH) in photo-Fenton system had the more highly catalytic degradation capacity to Acid Orange II (AOII) under an optimal condition (7.5 mmol/L of H₂O₂ oxidant, 40 mg/L of AOII, 0.2 g/L of catalyst dosage, and pH 4.0). The AOII degradation kinetics could be well fitted by pseudo-first-order model. In photo-Fenton catalytic process of AOII dye, the ∙OH and h⁺ were the main reaction substances. The AOII in solutions could be gradually mineralized into non-toxic inorganic H₂O molecule and CO₂. The β-FeOOH/PANI catalyst also had a good reusable ability of about 91.4% AOII degradation after 4 runs. These results can provide a reference for synthesis of catalyst used in photo-Fenton system and the applications in degradation removal of organic dye from wastewaters.

Heterogeneous Fenton oxidation of 2,4-dichlorophenol catalyzed by PEGylated nanoscale zero-valent iron supported by biochar

The excessive use of herbicides and fungicides containing 2,4-dichlorophenol (2,4-DCP) has led to serious environmental water pollution; 2,4-DCP is chemically stable and difficult to be degraded effectively by biological and physical methods. And the degradation of 2,4-DCP using advanced oxidation techniques has been a hot topic. Biochar, polyethylene glycol, ferrous sulfate, and sodium borohydride were used to synthesize the heterogeneous catalyst PEGylated nanoscale zero-valent iron supported by biochar (PEG-nZVI@BC). The catalyst was characterized using scanning electron microscope (SEM) and other means to determine its physicochemical properties. Catalytic performance and mechanism of this catalyst with hydrogen peroxide for the oxidation of 2,4-DCP were investigated. The results showed that PEG-nZVI@BC had good dispersibility, stability, and inoxidizability; the degradation efficiency of 50 mg/L 2,4-DCP by PEG-nZVI@BC/H₂O₂ system 92.94%, 1.68 times higher than that of nZVI/H₂O₂ system; there are both free radical and non-free radical pathways in PEG-nZVI@BC/H₂O₂ system; the degradation process of 2,4-DCP includes hydroxylation, dechlorination, and ring-opening. Overall, PEG-nZVI@BC is a promising heterogeneous catalyst for the degradation of 2,4-DCP.

Photolysis and cytotoxicity of the potentially toxic composition of daylily flower: colchicine

The photolysis of colchicine under ultraviolet and visible light irradiation was studied by ultraviolet (UV) scanning and HPLC-MS. The photoproduct was proposed and the cytotoxicity change before and after irradiation was investigated. Results showed that both ultraviolet and visible light irradiation could effectively degrade colchicine into deacetamido-lumicolchicine. The process conformed to first-order kinetics, in which a high degradation rate (K = 0.5862 h^− 1) was observed when colchicine was dissolved in ethanol and irradiated by UV light. Cell viability and cell cycle studies proved that a photolysis treatment of colchicine could weaken the cytotoxicity effectively. Colchicine inhibited the division of BRL 3 A cells in G2/M phase with an IC₅₀ value of 0.48 µg/mL, while the toxic effect could be reduced significantly with IC₅₀ 2.1 µg/mL when colchicine was exposed to UV irradiation. Results are beneficial to the toxicity elimination of colchicine in the processing of daylily flower in food industry, and can also provide photochemistry reference for colchicine-related studies.

Plasma Ag-Modified α-Fe2O3/g-C3N4 Self-Assembled S-Scheme Heterojunctions with Enhanced Photothermal-Photocatalytic-Fenton Performances

Low spectral utilization and charge carrier compounding limit the application of photocatalysis in energy conversion and environmental purification, and the rational construction of heterojunction is a promising strategy to break this bottleneck. Herein, we prepared surface-engineered plasma Ag-modified α-Fe₂O₃/g-C₃N₄ S-Scheme heterojunction photothermal catalysts by electrostatic self-assembly and light deposition strategy. The local surface plasmon resonance effect induced by Ag nanoparticles broadens the spectral response region and produces significant photothermal effects. The temperature of Ag/α-Fe₂O₃/g-C₃N₄ powder is increased to 173 °C with irradiation for 90 s, ~3.2 times higher than that of the original g-C₃N₄. The formation of 2D/2D structured S-Scheme heterojunction promotes rapid electron-hole transfer and spatial separation. Ternary heterojunction construction leads to significant enhancement of photocatalytic performance of Ag/α-Fe₂O₃/g-C₃N₄, the H₂ photocatalytic generation rate up to 3125.62 µmol g^-1 h^-1, which is eight times higher than original g-C₃N₄, and the photocatalytic degradation rate of tetracycline to reach 93.6%. This thermally assisted photocatalysis strategy improves the spectral utilization of conventional photocatalytic processes and provides new ideas for the practical application of photocatalysis in energy conversion and environmental purification.

Surface oxygen vacancies and carbon dopant co-decorated magnetic ZnFe2O4 as photo-Fenton catalyst towards efficient degradation of tetracycline hydrochloride

Carbon doped strategy has been recognized as an efficient strategy to enhance photo-Fenton degradation performance. However, the preparation of high efficiency C-doped photocatalyst has been a significant challenge. Herein, we synthesized magnetic carbon-doped ZnFe₂O₄ via a facile solvothermal-calcination route. The photo-Fenton activity of C-doped ZnFe₂O₄ under visible light (λ > 420 nm) was evaluated by degradation of tetracycline hydrochloride. C-doped sample, CZF-2 (0.5 g L^-1) presented excellent removal performance for TC-HCl (20 mg L^-1) in presence of H₂O₂ (10 mM) and could remove 90.8% of TC-HCl within 50 min. The C-doping modulates crystal defects and generates surface oxygen vacancies simultaneously, thus building a new C-doping level near valence band and a defect level under the conduction band. Meanwhile, surface oxygen vacancies bring photo-generated electrons and electrons generated from itself to surface to accelerate photo-Fenton reaction, and the holes are rapidly transferred to the surface to participate in the degradation of pollutants.

Enhanced photodegradation of decabromodiphenyl ether on oxygen vacancy-enriched Bi2MoO6

Debromination is a primary and critical procedure in the treatment of polybrominated diphenyl ethers (PBDEs) in the environment. Herein, oxygen vacancy-enriched Bi2MoO6 is firstly applied in the photoreduction debromination of PBDEs under visible light illumination. The introduction of oxygen vacancies not only promotes the red-shift of the light absorption band by Bi2MoO6, but also activates the C-Br bond through the formation of Br-O halogen bonds, thus realizing efficient visible light reduction of decabromodiphenyl ether (BDE209). The activation adsorption mode inferred by tracking analysis of the degradation process shows that the meta-position adsorption mode is the main adsorption configuration during the activation process, while the ortho-position adsorption mode is the most difficult. Thence, the oxygen vacancy-dominated photocatalytic BDE209 process is a position-selective multi-electron reduction process. The study shows that oxygen vacancy assisted C-Br activation is an excellent strategy for photocatalytic treatment of halogenated persistent organic pollutants.

S-scheme BiVO4/CQDs/β-FeOOH photocatalyst for efficient degradation of ofloxacin: Reactive oxygen species transformation mechanism insight

Photocatalysis technology exhibited promising application for advanced treatment of wastewater. Nevertheless, the design of efficient photocatalyst and the mechanism of free radicals in pollutant degradation still remained to be further investigated. Herein, BiVO₄/CQDs/β-FeOOH photocatalyst was fabricated by electrostatic self-assembly method, which exhibited the excellent photocatalytic performance. Under visible-light irradiation, the removal rate of ofloxacin by BiVO₄/CQDs/β-FeOOH (0.25 min^-1) was 1.93 times than pristine BiVO₄, and the removal efficiency in 15 min reached 99.21%. The perfect reusability of BiVO₄/CQDs/β-FeOOH was ascribed to the persistent catalytic active centers provided by the renewable surface oxygen vacancies on the β-FeOOH. As electron transfer channels, CQDs facilitated the transfer of BiVO₄ photogeneration electrons. The matched band structure allowed the construction of S-scheme heterojunctions, and the higher conduction band position was retained while the carrier separation was promoted. More importantly, this work firstly reported the phenomenon that the main reactive groups in the photocatalysis process would be directionally transformed with the change of pH conditions. Based on the analysis of capture and electron paramagnetic resonance experiments, ·O₂^- was the main free radicals to photodegrade OFL in neutral and alkaline conditions. However, when the solution pH turned into acidic, the photodegradation of OFL was dominated by ¹O₂. This innovative phenomenon was due to that acidic condition accelerated the reaction kinetics of spontaneous transformation of ·O₂^- to ¹O₂ and inhibited the direct oxidation of pollutants by ·O₂^-. Accordingly, this research could inspire theoretical study of free radical reaction and the design of S-scheme heterojunction photocatalysts.

MOF-derived N-doped ZnO carbon skeleton@hierarchical Bi2MoO6 S-scheme heterojunction for photodegradation of SMX: Mechanism, pathways and DFT calculation

Semiconductor photocatalytic degradation of pollutants is considered to be one of the promising sustainable energy routes. Nevertheless, it is challenging for photocatalysts to have excellent visible light absorption and suppress photo-generated electron-hole recombination at the same time. Here, we prepared nitrogen-doped ZnO carbon skeleton by directly calcining the metal-organic framework. Then hierarchical Bi₂MoO₆ nanosheets are grown in situ on its surface to synthesize S-scheme heterojunction. This special 3D layered and oxygen vacancies work together to make photo-generated electrons and holes easier to separate and migrate. Therefore, the pseudo-first-order kinetic constant of N-doped ZnO carbon skeleton@Bi₂MoO₆ degradation of sulfamethoxazole reaches 0.022 min^-1, which is almost 10 times that of ZIF-8 derived ZnO and 27.5 times Bi₂MoO₆ under visible light irradiation. Meanwhile, the mechanism of driving charge transfer of S-scheme heterojunction, and the photocatalytic degradation pathway of sulfamethoxazole are also analyzed. This work will provide a new way to construct S-scheme heterojunction photocatalyst to degrade antibiotic pollutants.

Photo-Fenton and oxygen vacancies' synergy for enhancing catalytic activity with S-scheme FeS2/Bi2WO6 heterostructure

A series of FeS2/Bi2WO6 S-scheme photo-Fenton catalysts with efficient catalytic performances were successfully prepared by coupling FeS2 into the surface oxygen vacancy enriched Bi2WO6 using calcination and solvothermal methods.

Construction of a novel two-dimensional AgBiO3/BiOBr step-scheme heterojunction for enhanced broad-spectrum photocatalytic performance

Efficient S-scheme heterojunction photocatalysts were prepared through in situ growth of AgBiO3 on BiOBr.

Alkylpolyglycoside modified MnFe2O4 with abundant oxygen vacancies boosting singlet oxygen dominated peroxymonosulfate activation for organic pollutants degradation

A novel alkylpolyglycoside (APG)-modified MnFe₂O₄ nanocomposite (APG@MnFe₂O₄) enriched with oxygen vacancies (VOs) was developed via co-precipitation and characterized as a peroxymonosulfate (PMS) activator to degrade 2,4-dichlorophenol (2,4-DCP) as the model contaminant. The APG effectively promoted the in situ formation of VOs on MnFe₂O₄ and subsequently enhanced the production of singlet oxygen (¹O₂). Furthermore, the APG@MnFe₂O₄ initialized an even more efficient non-radical pathway and dominated the degradation of 2,4-DCP. The constructed APG@MnFe₂O₄ exhibited a much higher reaction rate constant (0.0522) by ~12.73 times of that of the bare MnFe₂O₄ (0.0041). The degradation efficiency of 2,4-DCP in the APG@MnFe₂O₄/PMS system approached 93% within 90 min, a rate significantly higher than that in the MnFe₂O₄/PMS system (32%) given the same condition. The reasonable catalytic mechanism can be attributed to the Fe/Mn/VOs species. The APG@MnFe₂O₄ also exhibits universally high removal activity for various pollutants and excellent cyclic stability. Thus, the APG@MnFe₂O₄ is a promising PMS activator, and its utilization offers a useful strategy for developing VOs-enriched MnFe₂O₄ catalysts as a means of eliminating organic pollutants from wastewater.

Facile Vacuum Annealing-Induced Modification of TiO2 with an Enhanced Photocatalytic Performance

In this work, the photocatalytic performance enhancement of hydrothermally prepared TiO₂ was achieved by facile vacuum annealing treatment. Calcination of TiO₂ powder in air (CA-TiO₂) maintained its white color, while gray powder was obtained when the annealing was performed under vacuum (CV-TiO₂). Fourier transform infrared, total organic carbon, X-ray photoelectron spectroscopy, and electron paramagnetic resonance analyses proved that vacuum annealing transformed ethanol adsorbed on the surface of TiO₂ into carbon-related species accompanied by the formation of surface oxygen vacancies (Vo). The residual carbon-related species on the surface of CV-TiO₂ favored its adsorption of organic dyes. Compared with TiO₂ and CA-TiO₂, CV-TiO₂ exhibited an improved charge carrier separation with surface Vo as trapping sites for electrons. Vacuum annealing-induced improvement of crystallinity, enhancement of adsorption capacity, and formation of surface Vo contributed to the excellent photocatalytic activity of CV-TiO₂, which was superior to that of commercial TiO₂ (P25, Degussa). Obviously, vacuum annealing-triggered decomposition of ethanol played an important role in the modification of TiO₂. In the presence of ethanol, vacuum annealing was also suitable for the introduction of Vo into P25. Therefore, the current work offers an easy approach for the modification of TiO₂ to enhance its photocatalytic performance by facile vacuum annealing in the presence of ethanol.

Assembly of CaIn2S4 on Defect-Rich BiOCl for Acceleration of Interfacial Charge Separation and Photocatalytic Phenol Degradation via S-Scheme Electron Transfer Mechanism

The novel 2D/2D S-scheme heterostructure of BiOCl nanosheets coupled with CaIn2S4 nanosheets (CaIn2S4/BiOCl-SOVs), which contains surface oxygen vacancies (SOVs), has been successfully prepared by high-temperature calcination combined with a solvothermal synthetic strategy. Under visible-light irradiation, the apparent rate constant (Kapp/mim−1) for phenol degradation on the 1 wt% CaIn2S4/BiOCl-SOVs photocatalyst is about 32.8 times higher than that of pure BiOCl. The superior performance was attributed to the synergistic effect between the SOVs, CaIn2S4, and BiOCl, which can effectively narrow the bandgap and accelerate the interfacial charge separation of CaIn2S4/BiOCl-SOVs heterojunctions. Subsequently, it significantly promotes the generation of superoxide radicals (O2−), hydroxyl radicals, and h+, which participate in the photodegradation process of phenol. The catalyst still maintained a relatively high activity after repeated tests as a demonstration of its photostability. This work successfully proposed an efficient method to design a new 2D/2D S-scheme heterostructure with SOVs as possible photocatalysts in the field of environmental remediation.

Recent Advances in Covalent Organic Frameworks for Heavy Metal Removal Applications

Covalent organic frameworks comprise a unique class of functional materials that has recently emerged as a versatile tool for energy-related, photocatalytic, environmental, and electrochromic device applications. A plethora of structures can be designed and implemented through a careful selection of ligands and functional units. On the other hand, porous materials for heavy metal absorption are constantly on the forefront of materials science due to the significant health issues that arise from the release of the latter to aquatic environments. In this critical review, we provide insights on the correlation between the structure of functional covalent organic frameworks and their heavy metal absorption. The elements we selected were Pb, Hg, Cr, Cd, and As metal ions, as well as radioactive elements, and we focused on their removal with functional networks. Finally, we outline their advantages and disadvantages compared to other competitive systems such as zeolites and metal organic frameworks (MOFs), we analyze the potential drawbacks for industrial scale applications, and we provide our outlook on the future of this emerging field.

Self-Assembly of Nanosheet-Supported Fe-MOF Heterocrystals as a Reusable Catalyst for Boosting Advanced Oxidation Performance via Radical and Nonradical Pathways

Heterojunction catalysts have drawn increasing interest for the visible light-driven Fenton reaction and bring tremendous opportunities for environmental remediation. Herein, a BiOI/MIL-53(Fe) Z-scheme heterojunction (named BMFe) was synthesized for the first time via a facile strategy. Compared with pristine BiOI and MIL-53(Fe) catalysts, the two-dimensional/three-dimensional (2D/3D) heterojunction catalyst manifested remarkable catalytic performance toward degradation of phenol, bisphenol A, methylene blue, and carbamazepine, which is attributed mainly to the interfacial integration and efficient charge separation. By virtue of coupling at the interface, as confirmed by XPS, ⁵⁷Fe Mössbauer spectroscopy, and DFT calculations, the BMFe catalyst promoted the transfer of electron-hole pairs via Z-scheme and improved the chemical activation of hydrogen peroxide. The subsequent holes, free radicals, and nonradicals can effectively and continuously decompose pollutants, achieving a positive synergistic effect between photocatalysis and Fenton reactions. Simultaneously, the specially designed BiOX(X = Br, Cl)/MIL-53(Fe) and BiOI/Fe-MOFs(MIL-101, MIL-88) heterojunctions also exhibited advanced oxidative capacity for organic pollutants. Given their practical value for industrial applications, BMFe beads (1.0 ± 0.15 mm) synthesized via a blend cross-linking method can significantly advance long-term stability and recyclability. The integration of Fe-based metal-organic frameworks with bismuth oxyhalide semiconductors provides a new perspective on developing heterojunction catalysts for environmental remediation.

Covalent organic frameworks as robust materials for mitigation of environmental pollutants

Today, one of the main leading global problems is the presence of different pollutants in the environment. These pollutants not only affect human health but also overshadow the life of other creatures. Thus, pollutant treatment has become a challenging issue among the researchers and the scientific community. Different adsorbents and catalysts have been applied to the removal of pollutants. However, the associated limitations like poor chemical and physical stability, low surface area and low binding capacity revived researchers' attention to exploring alternative materials. Covalent organic frameworks (COFs) are versatile materials created based on the strong covalent interactions between blocked monomers. Unique features, including high specific surface area, high chemical-physical stability and crystallinity render COFs an intriguing sorbent and catalyst in treating pollutants. This review spotlights the applications of COFs as distinguished adsorbents to remove hazardous pollutants from the environment. At first, COFs and their properties as alternative materials were introduced. Then, different synthesis approaches of COFs and their advantages and disadvantages were discussed. Furthermore, the applications of COFs outlined to remove a wide variety of pollutants based on adsorption and degradation. Finally, the prospects of COFs for the treatment of pollutants were evaluated.

Novel Magnetic Fe3O4/α-FeOOH Nanocomposites and Their Enhanced Mechanism for Tetracycline Hydrochloride Removal in the Visible Photo-Fenton Process

Magnetic Fe₃O₄/α-FeOOH heterojunction nanocomposites (denoted as Fe-NCs) have been synthesized by a fast one-pot hydrothermal method. The obtained Fe-NCs contain rich micropores with a high surface area of 135.15 m²/g. The different phases in the composites can efficiently enhance the visible-light absorption, improving the separation and transfer of photogenerated electron-hole pairs during the photocatalytic reaction. Thus, they show excellent degradation and mineralization of tetracycline (TC) over a wide pH range (5-9) in the visible photo-Fenton reaction. Especially, the catalyst exhibits the highest adsorption capacity toward TC at a neutral pH, which facilitates the surface reactions of TC with active species. Experiments evidence that the high production of photogenerated holes and superoxide radicals (O₂ ^•-) in Fe-NCs are favorable to the high catalytic efficiency. Combined with liquid chromatography-mass spectrometry, the possible pathway toward TC degradation was proposed.

Review on the hazardous applications and photodegradation mechanisms of chlorophenols over different photocatalysts

Chlorophenols are very important environmental pollutants, which have created huge problems for both aquatic and terrestrial lives. Therefore, their removal needs urgent, effective, and advanced technologies to safeguard our environment for future generation. This review encompasses a comprehensive study of the applications of chlorophenols, their hazardous effects and photocatalytic degradation under light illumination. The effect of various factors such as pH and presence of different anions on the photocatalytic oxidation of chlorophenols have been elaborated comprehensively. The production of different oxidizing agents taking part in the photodegradation of chlorophenols are given a bird eye view. The photocatalytic degradation mechanism of different chlorophenols over various photocatalyts has been discussed in more detail and elaborated that how different photocatalysts degrade the same chlorophenols with the aid of different oxidizing agents produced during photocatalysis. Finally, a future perspective has been given to deal with the effective removal of these hazardous pollutants from the environment.

The construction of NiFeSx/g-C3N4 composites with high photocatalytic activity towards the degradation of refractory pollutants

In this work, a novel NiFe layered double hydroxide-derived sulfide (NiFeSx)-modified g-C3N4 nanosheet photocatalyst (NiFeSx/g-C3N4) was synthesized, and its morphology, structure and visible light absorption capacity were simultaneously characterized by XRD, SEM, TEM, FT-IR, XPS, UV-Vis DRS, PL techniques and EIS Nyquist plots. Furthermore, it was discovered that at an optimum mass ratio of 3% (NiFeSx to g-C3N4), 3% NiFeSx/g-C3N4 composites exhibited the best degradation efficiency toward tetracycline hydrochloride refractory pollutants. The degradation rate of tetracycline hydrochloride by 3% NiFeSx/g-C3N4 composites was 92.54% under 70 min of visible light illumination, which was about 2.61 times higher than that of pure g-C3N4. The improved degradation activity may be attributed to the synergistic effect between the two constituents of as-synthesized composites, and the formed heterojunction reduced the efficiency of photogenerated carriers. More importantly, this work also gives some inspiration to synthesize some similar photocatalysts for a targeted environmental remediation.

Insight into the key factors in fast adsorption of organic pollutants by hierarchical porous biochar

Low-cost biochar adsorbent owning great potential for environmental remediation faces a bottleneck in application for its unsatisfied adsorption performance. Compared to the efforts on increasing adsorption capacity, improving adsorption speed which is important for treatment efficiency is often neglected. Herein, a hierarchical porous biochar (HPB) derived from shrimp shell was prepared and exhibited good adsorption capacity (Q_m>300 mg/g) and fast adsorptive equilibrium (≤10 min) towards three typical aromatic organics, whose adsorption universality was further proved by two-way ANOVA analysis. Whereafter, model analysis demonstrated that, the adsorptive forms (mono- and multi-layers) on HPB depended on whether the contaminant is charged. Compared to the benzene-ring site of organics, the charged site contributed 5.13 times to adsorption promotion in monolayer but -0.49 times in inhibition for multilayers forms. Simultaneously, functional group sites contributed relatively weak (0.023 to 0.342 times only). Following structural control revealed that, hierarchical pore structure of HPB was the key for the fast adsorption speed, and highly graphitic structure was important for the high adsorption capacity. This study aims to provide an advanced biochar adsorbent, not only in adsorption capacity but also in adsorptive speed, and reveal the relationship between the structure and adsorption performance of biochar.