AgI loading BiOI composites with enhanced photodegradation efficiency for bisphenol A under simulated solar light

Fabrication, characterization, and application of BiOI@ZIF-8 nanocomposite for enhanced photocatalytic degradation of acetaminophen from aqueous solutions under UV-vis irradiation

This work investigates the use of novel BiOI@ZIF-8 nanocomposite for the removal of acetaminophen (Ace) from synthetic wastewater. The samples were analyzed using FTIR, XRD, XPS, DRS, PL, FESEM-EDS, and ESR techniques. The effects of the loading capacity of ZIF-8 on the photocatalytic oxidation performance of bismuth oxyiodide (BiOI) were studied. The photocatalytic degradation of Ace was maximized by optimizing pH, reaction time and the amount of photocatalyst. On this basis, the removal mechanisms of the target pollutant by the nanocomposite and its photodegradation pathways were elucidated. Under optimized conditions of 1 g/L of composite, pH 6.8, and 4 h of reaction time, it was found that the BiOI@ZIF-8 (w/w = 1:0.01) nanocomposite exhibited the highest Ace removal (94%), as compared to that of other loading ratios at the same Ace concentration of 25 mg/L. Although this result was encouraging, the treated wastewater still did not satisfy the required statutory of 0.2 mg/L. It is suggested that the further biological processes need to be adopted to complement Ace removal in the samples. To sustain its economic viability for wastewater treatment, the spent composite still could be reused for consecutive five cycles with 82% of regeneration efficiency. Overall, this series of work shows that the nanocomposite was a promising photocatalyst for Ace removal from wastewater samples.

Construction of type-II scheme SnO@HfC photocatalyst for bisphenol A degradation via peroxymonosulfate activation; DFT and self-cleaning analysis

In this study, novel stannous oxide@hafnium carbide (SnO@HfC) nanocomposite was successfully manufactured by an appropriate hydrothermal scheme which was utilized for the photocatalytic degradation of BPA by stimulation of peroxymonosulfate (PMS) and self-cleaning application. Numerous methods were applied for the characterization of photocatalyst and demonstrated the successful preparation of SnO@HfC nanocomposite. The crystal structures, band structures and density of states for SnO and HfC were explored by DFT analysis. The amazing PMS stimulation performance of SnO@HfC nanocomposite originated from the establishment of a heterojunction, which led to the enhancement of the light response aptitude and the electron conduction competence of the composite. BPA was degraded by 0.75 g/L PMS and SnO@HfC at neutral pH during the period of 60 min. In order to identify active groups in the reaction procedure, quenching experiments and electron paramagnetic resonance (EPR) approaches were also used. In the subsequent active species scavenging assays, where sulfate radicals, hydroxyl radicals, holes, and superoxide radicals were engaged in the degradation of BPA. While, liquid phase mass spectrometry (LC-MS) was used to pinpoint the intermediate metabolites in the course of degradation. SnO@HfC/PMS/light system delivered excellent TOC removal efficiency and less ions leaching. The SnO@HfC nanocomposite proved good durability and reusability in continuous cycle tests along with excellent self-cleaning function on the glass substrate. The SnO@HfC nanocomposite performs admirably in terms of self-cleaning application. The SnO@HfC nanocomposite is expected to be used in the future for the treatment of wastewater that contains pharmaceuticals due to its superior stability and reusability after five consecutive cycles.

Visible-light-driven AgI/Bi4O5I2 S-scheme heterojunction for efficient tetracycline hydrochloride removal: Mechanism and degradation pathway

The existence of excessive tetracycline hydrochloride (TCH) in the ecological environment has seriously threatened human health, so there is an urgent need to develop a high-performance photocatalyst that can efficiently and greenly remove TCH. Currently, most photocatalysts have the problems of fast recombination of photogenerated charge carriers and low degradation efficiency. Herein, S-scheme AgI/Bi₄O₅I₂ (AB) heterojunctions was constructed for TCH removal. Compared with the single component, the apparent kinetic constant of the 0.7AB is 5.6 and 10.2 time as high as the AgI and Bi₄O₅I₂, and the photocatalytic activity only decreases by 3.0% after four recycle runs. In addition, to verify the potential practical application of the fabricated AgI/Bi₄O₅I₂ nanocomposite, the photocatalytic degradation of TCH was performed under different conditions by regulating the dosage of photocatalyst, the TCH concentration, pH, and the existence of various anions. Systematical characterizations are conducted to investigate the intrinsic physical and chemical properties of the constructed AgI/Bi₄O₅I₂ composites. Based on the synergetic characterizations by in situ X-ray photoelectron spectroscopy, band edge measurements, as well as reactive oxygen species (ROS) detections, the S-scheme photocatalytic mechanism is proved. This work provides a valuable reference for developing efficient and stable S-scheme AgI/Bi₄O₅I₂ photocatalyst for TCH removal.

Novel Z-scheme AgI/Sb2WO6 heterostructure for efficient photocatalytic degradation of organic pollutants under visible light: Interfacial electron transfer pathway, DFT calculation and mechanism unveiling

Developing highly efficient heterostructured photocatalysts with robust redox ability is of great significance to wastewater purification. Herein, a novel Z-scheme AgI/Sb2WO6 heterojunction was successfully constructed via a chemical-precipitation method. The Z-scheme system can serve as a highly efficient photocatalyst for degradation of organic pollutants in water. Under visible light illumination, the degradation efficiency of rhodamine B and tetracycline over the optimal Z-scheme heterojunction can achieve 95% in 12 min and 80% in 8 min, which is 10.8 and 11.4 times higher than that over single Sb2WO6, respectively. Interestingly, low amounts of Ag0 can be generated and attached on the surface of Sb2WO6 during the photocatalytic process, further enhancing the photocatalytic activity of the Z-scheme heterojunction. Based on theoretical calculations, the interfacial internal electric field (IEF) can facilitate the photoexcited electrons at the conduction band (CB) of AgI to consume the photoexcited holes at the valence band (VB) of Sb2WO6, which greatly promotes the Z-scheme charge transfer path. Quenching experiments and electron spin resonance analyses demonstrate superoxide radicals play a major role in the photocatalytic reactions. The concept of constructing a Z-scheme heterojunction photocatalyst with efficient interfacial charge transfer shall provide a design guide for wastewater purification.

The boosted activity of AgI/BiOI nanocatalyst: a RSM study towards Eriochrome Black T photodegradation

Nowadays, critical environmental pollution needs some novel, simple, effective, and cost-effective catalysts with high efficiency in the visible region of the light. Thus, the AgI/BiOI coupled nanocatalyst sample (CS) was prepared and briefly characterized. The pH_pzc values of 6.2, 5.4, and 4.5 were estimated for AgI, BiOI, and AgI/BiOI samples. Based on the PXRD results, average crystallite sizes of 35.2, 34.7, and 34.1 nm were obtained for AgI, BiOI, and AgI/BiOI samples from the Scherrer formula and 38.3, 25.6, and 25.6 nm by the Williamson-Hall formula. SEM image confirmed a sheet-like BiOI morphology covered by AgI nanoparticles. The simultaneous interactions of the influencing variables on the boosted photocatalytic activity of CS sample towards Eriochrome Black T (EBT) were evaluated by response surface methodology (RSM) (under 100-W tungsten lamp irradiation with 230 mW/m².nm irradiance). The goodness of the model was confirmed by the significance of the model (F value of 65.68 > F_{0.05, 14, 13} = 2.55) and a non-significant LOF (F value of 0.97 < F_{0.05, 10, 3} = 8.79) at a 95% confidence interval obtained in ANOVA analysis of the results. The center point runs have the following conditions: catalyst dose: 0.68 g/L; pH: 7.5; C_EBT: 7.25 mg/L; and irradiation time: 53.5 min, while the optimal run included the following conditions: catalyst dose: 1.0 g/L; pH: 4; C_EBT: 10 mg/L; and irradiation time: 80 min. About 95% of EBT molecules were degraded in the optimal conditions.

Enhanced photocatalytic degradation of bisphenol A by magnetically separable bismuth oxyiodide magnetite nanocomposites under solar light irradiation

Bismuth oxyiodide/magnetite (BiOI/Fe₃O₄) nanocomposites were synthesized by a hydrothermal reaction. The synthesized BiOI/Fe₃O₄ was used to remove bisphenol A (BPA) from an aqueous solution under simulated solar light. The molar ratio of Bi to Fe in BiOI/Fe₃O₄ significantly affected BPA degradation, with the optimal BiOI/Fe₃O₄ (2:1) ratio in the composites. Optimum operating conditions such as a catalyst dosage of 1.0 g/L, an initial BPA concentration of 10 mg/L, and pH 7 gave a complete degradation of completely removed BPA within 30 min. The primary reactive oxygen species were verified as superoxide radicals and holes in oxidative species experiments. The magnetic BiOI/Fe₃O₄ could be easily collected from an aqueous solution by an external magnet, and its reusability was successfully demonstrated through recycling experiments. Furthermore, the derivatives in BiOI/Fe₃O₄ photocatalytic reactions were investigated, and a possible BPA degradation pathway was proposed. These results show that BiOI/Fe₃O₄ nanocomposites have great potential for BPA removal from water and wastewater treatment systems.

A high-efficiency mediator-free Z-scheme Bi2MoO6/AgI heterojunction with enhanced photocatalytic performance

A high-efficiency Z-scheme Bi₂MoO₆/AgI heterojunction was designed and fabricated via in situ growth of AgI on Bi₂MoO₆. Its photocatalytic activity was investigated with the degradation of malachite green (MG). After 40 min of visible light irradiation, near complete degradation of MG (20 mg/L) occurred when BA11 (Bi₂MoO₆:AgI = 1:1, 2.0 g/L) was present, while only 29.0% and 49.7% of the MG could be degraded in the presence of Bi₂MoO₆ and AgI, respectively. The excellent photocatalytic activity of BA11 results from strong visible light absorption and the low recombination efficiency of photogenerated electron-hole pairs induced by the formation of heterojunction. Density function theory (DFT) calculations revealed that the formation of built-in electric field at the interface between Bi₂MoO₆ and AgI facilitates the effective separation and transfer of photogenerated charge carriers. Results of reuse experiments indicated that the heterostructured photocatalyst has excellent stability. Radical scavenging experiments and electron spin resonance spectra showed that superoxide radicals (O₂^-) and hydroxyl radicals (OH) were the major reactive oxygen species in the photocatalytic system. The photocatalytic degradation pathway of MG was proposed based on the organic degradation intermediates detected. These findings demonstrate that the mediator-free Z-scheme Bi₂MoO₆/AgI heterojunction could serve as a promising photocatalyst in photocatalytic treatment of organic pollutants.

Facile synthesis of Ag2O/ZnO/rGO heterojunction with enhanced photocatalytic activity under simulated solar light: Kinetics and mechanism

Ag₂O/ZnO/rGO heterojunction photocatalysts were synthesized via a rapid microwave hydrothermal method for photocatalytic degradation of bisphenol A (BPA) under simulated solar light. Ag doping efficiently decreased the bandgap of ZnO, and loading on rGO inhibited the recombination of photoinduced electron-hole pairs. The highest BPA removal rate (80%) was achieved with an Ag doping ratio of 5% and a GO loading ratio of 3 wt%. The enhanced photocatalytic performance was attributed to the narrower bandgap and the improved separation efficiency of electron-hole pairs. Moreover, the recycling experiments proved that Ag₂O/ZnO/rGO possessed excellent photostability. Hole (h⁺) and •OH played crucial roles in the photocatalytic system. The degradation pathway of BPA including hydroxylation and the cleavage of covalent bonds was proposed. The toxicity assessment of intermediates elucidated that most of intermediates were less toxic than BPA. The as-prepared Ag₂O/ZnO/rGO exhibited outstanding photostability and pH adaptability, having great potential to be applied to the degradation of emerging organic pollutants in wastewater.

Few-layer WS2 modified BiOBr nanosheets with enhanced broad-spectrum photocatalytic activity towards various pollutants removal

Herein, an efficient broad-spectrum WS₂/BiOBr heterostructure with ultrathin nanosheet was successfully prepared by one-pot hydrothermal route. The self-assembled flower-like WS₂/BiOBr nanostructure was formed by few-layer WS₂ and BiOBr nanosheets. The optimized heterojunction presented broad-spectrum high-efficiency photocatalytic activity towards the removal of various pollutants under visible-light irradiation, including organic dyes, antibiotics and phenols. This efficiency was linked to high light harvesting combined with effective charge separation/transfer. Meanwhile, the degradation efficiencies varied with nature of the pollutant decreased in the following order: LR5B (99%) > MNZ (97%) > TC (92%) > OTC (92%) > RhB (90%) > CIP (83%) > MB (78%) > MO (62%) > bisphenol (42%) > phenol (40%). The photocatalytic process of ciprofloxacin was explored, and the results indicated that high ciprofloxacin concentrations, low pH values and elevated concentrations of ions (PO₄^3-, HPO₄^2-, H₂PO₄^-, and Cu²⁺) restrained the photocatalytic performances. Trapping experiments and ESR revealed the significant contribution of holes (h⁺) in the mechanism, where both superoxide radicals (O₂^-) and hydroxyl radicals (OH) acted as assistants. Overall, this work could offer a new protocol for the design of highly efficient heterostructure photocatalysts for environmental remediation.