Noble metals (Pd, Ag, Pt, and Au) doped bismuth oxybromide photocatalysts for improved visible light-driven catalytic activity for the degradation of phenol.

The doping of noble metals onto the semiconductor metal oxides has a great impact on the intrinsic properties of the materials. This present work reports the synthesis of noble metals doped BiOBr microsphere by a solvothermal method. The various characteristic findings reveal the effective incorporation of Pd, Ag, Pt, and Au onto the BiOBr and the performance of synthesized samples was test for the degradation of phenol over visible light. The Pd-doped BiOBr material showed enhanced phenol degradation efficacy, which is ∼4-fold greater than pure BiOBr. This improved activity was on reason of good photon absorption, lower recombination rate, and higher surface area facilitated by surface plasmon resonance. Moreover, Pd-doped BiOBr sample displayed good reusability and stability after 3 cycles of run. A plausible charge transfer mechanism for phenol degradation is disclosed in detail over Pd-doped BiOBr sample. Our findings disclose that the incorporation of noble metal as the electron trap is a feasible approach to enhance visible light activity of BiOBr photocatalyst used in phenol degradation. This work represents new vision interested in the outline and development of noble metal doped semiconductor metal oxides as a visible light material for the elimination of colorless toxins from untreated wastewater.

Novel BiVO4-nanosheet-supported MoS2-nanoflake-heterostructure with synergistic enhanced photocatalytic removal of tetracycline under visible light irradiation.

This paper describes a simple in-situ hydrothermal technique for the production of BiVO4/MoS2 binary nanocomposites as visible-light-driven catalysts. The as-prepared samples were analyzed by structural, morphological, compositional, optical, surface area, and photocurrent analyses. The lattice fringe spaces at 0.304 nm and 0.612 nm were indexed to the (112) and (002) crystal planes of BiVO4 and MoS2, respectively. Antibacterial photocatalytic capabilities were assessed using tetracycline (TC). Consequently, it was observed that the BiVO4/MoS2 nanocomposite demonstrated improved antibacterial removal ability compared with the pristine samples. The BiVO4/MoS2 nanocomposite exhibited 97.46% removal of TC compared with the pure BiVO4 (43.76%) and MoS2 (35.28%) samples within 90 min. Thus, the photocatalytic performance was observed to follow the given order: BiVO4/MoS2 nanocomposite > BiVO4 > MoS2. The removal of TC after 90 min of irradiation was approximately 97.46%, 96.62%, 95.59%, and 94.45% after the 1st, 2nd, 3rd, and 4th cycles, respectively. Thus, the recycling tests revealed the stability of the photocatalyst, which exhibited a TC removal efficiency of 94.45% without distinct decay, even after the 4th cycle. According to the trapping results, hydroxyl radicals and holes were the key species and demonstrated a greater influence on the photocatalytic performance than superoxide radicals. The increased activity of the BiVO4/MoS2 nanocomposite may be attributed to its large surface area and tunable bandgap, which accelerate the charge-transport characteristics of the photocatalytic system. This insight and synergetic effects can provide a new approach for the development of novel heterostructure photocatalysts.

Synthesis of novel graphene aerogel encapsulated bismuth oxyiodide composite towards effective removal of methyl orange azo-dye under visible light.

Development of novel and eco-friendly composite photocatalysts for the efficient removal of contaminants from wastewater is the need of the hour. In this study, visible light responsive novel graphene aerogel/bismuth oxyiodide (GA/BiOI) composite was synthesized via low-temperature solvothermal method. The synthesized GA/BiOI composite was tested for methyl orange (MO) azo-dye degradation under visible light. The graphene aerogel nanosheets were wrapped onto the surface of the each individual BiOI microsphere, which encourages the interconnection charge transfer process. The light absorption properties of GA/BiOI composite were increased with the addition of graphene aerogel. The optimal 5%-GA/BiOI composite displayed higher MO removal efficiency, which is ∼2 fold more than the bare BiOI photocatalyst. This enhanced photocatalytic activity was on account of lower recombination rate of charge carriers, improved light absorption, and the high surface area. In addition, the 5%-GA/BiOI composite showed good stability until 3 cycles without deactivation. The plausible MO degradation mechanism was also proposed over GA/BiOI under visible light. This work provides a new perspective on the design and synthesis of graphene aerogel-based composite for environmental applications.

Effect of nonmetals (B, O, P, and S) doped with porous g-C3N4 for improved electron transfer towards photocatalytic CO2 reduction with water into CH4.

Photocatalytic conversion of carbon dioxide (CO2) into gaseous hydrocarbon fuels is an auspicious way to produce renewable fuels in addition to greenhouse gas emission mitigation. In this work, non-metals (B, O, P, and S) doped graphitic carbon nitride (g-C3N4) was prepared via solid-state polycondensation of urea for photocatalytic CO2 reduction into highly needed methane (CH4) with water under UV light irradiation. The various physicochemical characterization results reveal the successful incorporation of B, O, P, and S elements in the g-C3N4 matrix. The maximum CH4 yield of 55.10 nmol/(mLH2O.gcat) over S-doped g-C3N4 has been obtained for CO2 reduction after 7 h of irradiation. This amount of CH4 production was 1.9, 1.4, 1.7, and 2.4-folds higher than B, O, P and bare g-C3N4 samples. The doping of S did not enlarge the surface area and photon absorption ability of the g-C3N4 sample, but this significant improvement was evidently due to effective charge separation and migration. The observed results imply that the doping of non-metal elements provides improved charge separation and is an effective way to boost photocatalyst performance. This work offers an auspicious approach to design non-metal doped g-C3N4 photocatalysts for renewable fuel production and would be promising for other energy application.

Single-step fabrication of highly stable amorphous TiO2 nanotubes arrays (am-TNTA) for stimulating gas-phase photoreduction of CO2 to methane.

This study investigates the facile fabrication of interfacial defects assisted amorphous TiO2 nanotubes arrays (am-TNTA) for promoting gas-phase CO2 photoreduction to methane. The am-TNTA catalyst was fabricated via a one-step synthesis, without heat treatment, by anodization of Titanium in Ethylene glycol-based electrolyte in a shorter anodizing time. The samples presented a TiO2 nanostructured array with a nanotubular diameter of 100 ± 10 nm, a wall thickness of 26 ± 5 nm, and length of 3.7 ± 0.3 µm, resulting in a specific surface of 0.75 m2 g. The am-TNTA presented prolonged chemical stability, a high exposed surface area, and a large number of surface traps that can reduce the recombination of the charge carriers. The am-TNTA showed promising photoactivity when tested in the CO2 reduction reaction with water under UV irradiation with a methane production rate of 14.0 µmol gcat-1 h-1 for a pure TiO2 material without any modification procedure. This enhanced photocatalytic activity can be explained in terms of surface defects of the amorphous structure, mainly OH groups that can act as electron traps for increasing the electron lifetime. The CO2 interacts directly with those traps, forming carbonate species, which favors the catalytic conversion to methane. The am-TNTA also exhibited a high stability during six reaction cycles. The photocatalytic activity, the significantly reduced time for synthesis, and high stability for continuous CH4 production make this nanomaterial a potential candidate for a sustainable CO2 reduction process and can be employed for other energy applications.

Recent developments on bismuth oxyhalides (BiOX; X = Cl, Br, I) based ternary nanocomposite photocatalysts for environmental applications.

Photocatalytic treatment of organic pollutants present in wastewater using semiconductor nanomaterials under light irradiation is one of the efficient advanced oxidation processes. Stable metal oxide (e.g. TiO2) based semiconductor photocatalytic systems have been mainly investigated for this purpose. Nevertheless, their large band gap (~3.2 eV) makes them inefficient in utilization of visible light portion of solar light leading to a lower degradation efficiency. Investigations have focused on the development of visible light responsive bismuth oxyhalides (BiOX; X = Cl, Br, I), one of the potential nanomaterials with unique layered structure, for efficient absorption of solar light for the degradation of pollutants. However, the rapid recombination rate of photogenerated charge carriers limits their practical applicability. To overcome such drawbacks, the development of BiOX based ternary nanocomposites received significant attention because of their unique structural and electronic properties, improved visible light response and increased separation and transfer rate of photogenerated charge carriers. This review aims to provide a comprehensive overview of the recent developments on bismuth oxyhalides-based ternary nanocomposites for enhanced environmental pollutants decomposition under visible light irradiation. The principles of photocatalysis, synthetic methodologies of bismuth oxyhalides and their characteristics such as heterojunctions formation, improved visible light response and separation rate of charge carriers and the mechanisms for enhanced visible light photocatalytic activity are discussed. In addition, the future prospects on the improvement in the photocatalytic activity of bismuth oxyhalides-based ternary nanocomposites are also discussed. This review could be beneficial for designing new ternary nanocomposites with superior visible light photocatalytic efficiency.

Solvent-mediated synthesis of BiOI with a tunable surface structure for effective visible light active photocatalytic removal of Cr(VI) from wastewater.

The present study investigated the effect of various solvents on the tunable surface morphology and photocatalytic activity (PCA) of bismuth oxyiodide (BiOI), which could be used for the reduction of Cr(VI) under visible light irradiation (VLI). BiOI samples exhibiting different morphologies, i.e., two-dimensional square-like nanosheet and three-dimensional hierarchical flower-like morphology, were synthesized by a hydro/solvothermal process using different solvents, namely H2O, MeOH, EtOH, and ethylene glycol (EG). The crystal structure, surface morphology, surface area, light-absorption capability, and recombination rate of the photogenerated charge carriers were examined by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller analysis, UV-vis diffuse reflectance spectroscopy, photoluminescence, and transient photocurrent analyses, respectively. The BiOI sample fabricated in EG showed excellent photocatalytic efficiency (~99%) for the reduction of Cr(VI) after 90 min under VLI. The enhanced PCA demonstrated that the high surface area and well-structured surface characteristics of flower-like 3D BiOI microspheres played important roles in the photoreduction process. Moreover, a plausible mechanism for the reduction of Cr(VI) over the EG-BiOI photocatalyst was proposed. The results of the PCA evaluation and recycle test revealed that 3D EG-BiOI microspheres could serve as promising materials for the efficient removal of Cr(VI) from wastewater. Additionally, EG-BiOI could be utilized in other environmental remediation processes.

Enhanced photocatalytic activity at multidimensional interface of 1D-Bi2S3@2D-GO/3D-BiOI ternary nanocomposites for tetracycline degradation under visible-light.

Structural dimensionality and surface morphology are key properties that greatly affect the functionalities of materials. Herein, we report a synthesis of dimensionally coupled ternary nanocomposites from three-dimensional (3D) bismuth oxyiodide (BiOI), two-dimensional (2D) graphene oxide (GO), and one-dimensional (1D) bismuth sulfide (Bi2S3) nanomaterials for tetracycline degradation under visible-light irradiation. The 2%-Bi2S3@1%-GO/BiOI ternary nanocomposites show higher degradation efficiency than neat 3D-BiOI. The coupling of neat 1D-Bi2S3 with the 1%-GO/BiOI binary nanocomposite does not increase the specific surface area of the resulting 2%-Bi2S3@1%-GO/3D-BiOI ternary nanocomposite, but enhances notably its charge carrier separation and migration, according to the analysis of the higher photocurrent, smaller arc radius of the electrochemical impedance spectroscopy and lower photoluminescence intensity. The observed results suggest that the combination of dimensionally coupled composites provides a synergistic effect through an efficient charge transfer process. This work offers new insights into the design and construction of dimensionally coupled ternary nanocomposites for environmental remediation applications.