BiOmFn/BiOxIy/GO Nanocomposites: Synthesis, characterization, and photocatalytic activity

Efficient charge separation and improved photocatalytic activity in Type-II & Type-III heterojunction based multiple interfaces in BiOCl0.5Br0.5-Q: DFT and Experimental Insight

The nanostructured, inner-coupled Bismuth oxyhalides (BiOX_0.5X'_0.5; X, X' = Cl, Br, I; X≠X') heterostructures were prepared using Quercetin (Q) as a sensitizer. The present study revealed the tuning of the band properties of as-prepared catalysts. The catalysts were characterized using various characterization techniques for evaluating the superior photocatalytic efficiency and a better understanding of elemental interactions at interfaces formed in the heterojunction. The material (BiOCl_0.5Br_0.5-Q) reflected higher degradation of MO (about 99.85%) and BPA (98.34%) under visible light irradiation than BiOCl_0.5I_0.5-Q and BiOBr_0.5I_0.5-Q. A total of 90.45 percent of total organic carbon in BPA was removed after visible light irradiation on BiOCl_0.5Br_0.5-Q. The many-fold increase in activity is attributed to the formation of multiple interfaces between halides, conjugated π-electrons and multiple -OH groups of quercetin (Q). The boost in degradation efficiency can be attributed to the higher surface area, 2-D nanostructure, inhibited electron-hole recombination, and appropriate band-gap of the heterostructure. Photo-response of BiOCl_0.5Br_0.5-Q is higher compared to BiOCl_0.5I_0.5-Q and BiOBr_0.5I_0.5-Q, indicating better light absorption properties and charge separation efficiency in BiOCl_0.5Br_0.5-Q due to band edge position. First-principles Density Functional Theory (DFT) based calculations have also provided an insightful understanding of the interface formation, physical mechanism, and superior photocatalytic performance of BiOCl_0.5Br_0.5-Q heterostructure over other samples.

Rational design of ZnO-zeolite imidazole hybrid nanoparticles with reduced charge recombination for enhanced photocatalysis

Semiconducting zinc oxide nanoparticles (ZnO NPs) hold great potential as photocatalysts in wastewater treatment because of their favorable bandgap and cost-effectiveness. Unfortunately, ZnO NPs usually show rapid charge recombination that limits their photocatalytic efficacy significantly. Herein, we report a facile way of modifying ZnO NPs with zeolite imidazole framework-8 (ZIF8). A synergy between the two components may tackle the drawback of fast charge recombination for pristine ZnO NPs. Improved performance of photocatalytic degradation of methylene blue (MB) is confirmed by comparing with pristine ZnO and ZIF8 as the catalysts. The ZIF8 in the composite serves as a trap for photogenerated electrons, thus reducing the rate of charge recombination to enhance the photocatalysis rate. In addition, the hybridization process suppresses the aggregation of ZnO NPs, providing a large surface area and a greater number of active sites. Moreover, a small shift in the absorption band of ZnO@ZIF8 (10) NPs towards higher wavelength, also witnessed a little contribution towards enhanced photocatalytic properties. Mechanistic studies of the photocatalytic process of MB using ZnO@ZIF8 NPs catalyst reveal that hydroxyl radicals are the major reactive oxygen species. The facile hybridization of ZnO with ZIF8 provides a strategy for developing new photocatalysts with wide application potential.

Recent advancement in Bi5O7I-based nanocomposites for high performance photocatalysts

Bi₅O₇I belongs to the family of bismuth oxyhalides (BiOX, X = Cl, Br, I), having a unique layered structure with an internal electrostatic field that promotes the separation and transfer of photo-generated charge carriers. Interestingly, Bi₅O₇I exhibits higher thermal stability compared to its other BiOX member compounds and absorption spectrum extended to the visible region. Bi₅O₇I has demonstrated applications in diverse fields such as photocatalytic degradation of various organic pollutants, marine antifouling, etc. Unfortunately, owing to its wide band gap of ∼2.9 eV, its absorption lies mainly in the ultraviolet region, and a tiny portion of absorption lies in the visible region. Due to limited absorption, the photocatalytic performance of pure Bi₅O₇I is still facing challenges. In order to reduce the band gap and increase the light absorption capability of Bi₅O₇I, doping and formation of heterostructure strategies have been employed, which showed promising results in the photocatalytic performance. In addition, the plasmonic heterostructures of Bi₅O₇I were also developed to further boost the efficiency of Bi₅O₇I as a photocatalyst. Here, in this review article, we present such recent efforts made for the advanced development of Bi₅O₇I regarding its synthesis, properties and applications. The strategies for photocatalytic performance enhancement have been discussed in detail. Moreover, in the conclusion section, we have presented the current challenges and discussed possible prospective developments in this field.

Controlled hydrothermal synthesis of BiOxCly/BiOmBrn/g-C3N4 composites exhibiting visible-light photocatalytic activity

The first systematic synthesis of bismuth oxychloride/bismuth oxybromide/graphitic carbon nitride (BiO_xCl_y/BiO_mBr_n/g-C₃N₄) nano-composites used a controlled hydrothermal method. The structure, morphology and characteristic of BiO_xCl_y/BiO_mBr_n/g-C₃N₄ photocatalyst were measured by XRD, UV-vis-DRS, FT-IR, FE-TEM, FE-SEM-EDS, PL, BET, HR-XPS and EPR. Under visible light irradiation, the photodegradation activity was evaluated for the decolorization of crystal violet (CV) and 2-hydroxybenzoic acid (2-HBA) in aqueous solution. The catalytic performance showed that, when using sample BB2C1-4-250-30 wt% g-C₃N₄ composite as a photocatalyst, the best reaction-rate-constant (k) was 0.071 h^-1. It was 1.5 times higher than the k value of BB2C1-4-250 as a photocatalyst. From the scavenging effect of various scavengers, the results of EPR showed that reactive OH was the main scavenger, while O₂^-, h⁺ and ¹O₂ were the second scavenger in CV degradation. In this study, a possible photodegradation mechanism was proposed and discussed. In this work, our method of BiO_xCl_y/BiO_mBr_n/g-C₃N₄ preparation could be used for future mass production and the BiO_xCl_y/BiO_mBr_n/g-C₃N₄ composite materials could be applied to the environmental pollution control in future.

Energizing periodic mesoporous organosilica (PMOS) with bismuth and cerium for photo-degrading methylene blue and methyl orange in water

This work reported an efficient catalyst to reduce the organic pollutants by using an energetic periodic mesoporous organosilica (PMOS) supported with bismuth (Bi-PMOS) and cerium (Ce-PMOS). PMOS support was designed through co-condensation of sodium silicate and 3-methacryloxypropyltrimethoxysilane on polysorbate templates. The resultant PMOSs were fabricated with bismuth and cerium oxides to formulate Bi-PMOS and Ce-PMOS, respectively. These materials showed photo-degradations of methylene blue (MB, 74.7% and 41.1% with Bi-PMOS and Ce-PMOS, respectively) and methyl orange (MO, 53.2% and 39.4% with Bi-PMOS and Ce-PMOS, respectively). Such efficient photo-degradations were attributed to the precise doping of metallic nodes of Bi₂ O₃ and CeO₂ on the porous structure of PMOS with high surface area. The results also showed that Bi and Ce were more effective in PMOS support for photo-degradation of dyes as the support provides more lifetime to photo-generated electron-hole pairs than other materials. Moreover, active reusability and high degradation efficiencies of Bi-PMOS and Ce-PMOS proved them better analytical tools to reduce organic pollutants under visible lights. PRACTITIONER POINTS: The oxides of bismuth and cerium have impressive photocatalytic characteristics. New material energizing mesoporous organosilica with bismuth and cerium for photo-degradation of methylene blue and methyl orange in water. The use of an efficient catalyst to reduce the organic pollutants by using an energetic periodic mesoporous organosilica (PMOS) supported with bismuth (Bi-PMOS) and cerium (Ce-PMOS).

Bismuth-rich bismuth oxyiodide microspheres with abundant oxygen vacancies as an efficient photocatalyst for nitrogen fixation

A combined bismuth-rich and defect introduction strategy was used to prepare the H-Bi₅O₇I with abundant oxygen vacancies, which can effectively yield ammonia under visible light without any organic scavengers or noble-metal cocatalysts.

Bi4O5I2/nitrogen-doped hierarchical carbon (NHC) composites with tremella-like structure for high photocatalytic performance

BiOI is a visible photocatalyst towards organic pollutant. In this work, biomass waste (withered typha grass) was used to fabricate nitrogen-doped hierarchical carbon (NHC) by an one-step carbonization route. Then NHC provided a good carrier to load the BiOI semiconductor materials by a green simple co-precipitation method, after adding NaOH solution, the irregular microspheres BiOI/NHC was gradually etched by OH^- to form the tremella-like Bi₄O₅I₂/NHC. The well-defined tremella-like Bi₄O₅I₂/NHC invested adequate interface and high particular surface range (S_BET: 66 m² g^-1), which is higher than pure BiOI (22 m² g^-1) and Bi₄O₅I₂ (17 m² g^-1). Multiple synergistic effects, such as high S_BET can give more dynamic destinations, the special tremella-like structure can assimilate more reflected occurrence light of other nanosheets, low I content can increase the conduction/valence band gap of semiconductor materials and NHC can act as an electron acceptor, making as-prepared Bi₄O₅I₂/NHC composite ideal candidates for photocatalysis. The degradation rate of Bi₄O₅I₂/NHC reaches up to 87.4% of methyl orange in 2 h, which is about 2 times higher than BiOI and Bi₄O₅I₂. Therefore, this work gives a technique to link NHC derived from biomass waste to Bi₄O₅I₂ with highly-efficiency photocatalytic performance.

Composite Magnetic Photocatalyst Bi₅O₇I/MnxZn1-xFe₂O₄: Hydrothermal-Roasting Preparation and Excellent Photocatalytic Activity

A new composite magnetic photocatalyst, Bi₅O₇I/Mn_xZn_1-xFe₂O₄, prepared by a hydrothermal-roasting method was studied. The photocatalytic properties of Bi₅O₇I/Mn_xZn_1-xFe₂O₄ were evaluated by degradation of Rhodamine B (RhB) under simulated sunlight irradiation, and the structures and properties were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible light (UV-Vis) diffuse reflectance spectra (DRS), and a vibrating sample magnetometer (VSM). The results indicated that Bi₅O₇I/Mn_xZn_1-xFe₂O₄ was an orthorhombic crystal, which was similar to that observed for Bi₅O₇I. Bi₅O₇I/Mn_xZn_1-xFe₂O₄ consisted of irregularly shaped nanosheets that were 40⁻60 nm thick. The most probable pore size was 24.1 nm and the specific surface area was 7.07 m²/g. Bi₅O₇I/Mn_xZn_1-xFe₂O₄ could absorb both ultraviolet and visible light, and the energy gap value was 3.22 eV. The saturation magnetization, coercivity and residual magnetization of Bi₅O₇I/Mn_xZn_1-xFe₂O₄ were 3.9 emu/g, 126.6 Oe, and 0.7 emu/g respectively, which could help Bi₅O₇I/Mn_xZn_1-xFe₂O₄ be separated and recycled from wastewater under the action of an external magnetic field. The recycling experiments revealed that the average recovery rate of the photocatalyst was 90.1%, and the photocatalytic activity was still more than 81.1% after five cycles.

Photovoltaic and photocatalytic properties of bismuth oxyiodide-graphene nanocomposites

In this study, we evaluate the photovoltaic and photocatalytic properties of chemical vapor deposited bismuth oxyiodide (BiOI) and bismuth oxyiodide-graphene (BiOI-GR) nanocomposite thin films. The BiOI thin film has an average thickness of 574 nm and a bandgap of around 2 eV. The BiOI and BiOI-GR thin films exhibited nanoflake morphology. It was found that addition of graphene increases absorbance by causing vertical growth of nanoflakes, imparting anti-reflectance and light trapping properties. The photocatalytic activities of the thin films were evaluated by examining methylene blue (MB) degradation under visible light irradiation. BiOI-GR degraded 56.42% of MB in two hours while BiOI degraded 44.16%. Afterwards, FTO|BiOI|graphite|Al and FTO|BiOI-GR|graphite|Al solar cell devices were fabricated with photocurrent density values of 2.0 μA cm-2 and 2.7 μA cm-2, respectively. The improved properties of BiOI-GR are attributed to the anti-reflecting and light trapping properties of vertical BiOI-GR nanoflakes and the enhanced carrier separation due to graphene as an electron acceptor.