Enhanced photocatalytic performance of TiO2/BiOI heterojunctions benefited from effective separation of photogenerated carriers

BiOI/Bi2MoO6 p-n Junction to Enhance Visible Light Photocatalytic Activity toward Environmental Remediation

Photocatalytic degradation of organic pollutants via semiconductors with high visible light response and effective carrier separation is an economical and green route to greatly achieve environmental remediation. Herein, an efficient BiOI/Bi₂MoO₆ p-n heterojunction was in situ fabricated through hydrothermal method by substituting Mo₇O₂₄^6- species for I ions. The characteristic p-n heterojunction exhibited a strongly enhanced visible light responsive absorption from 500 to 700 nm owing to the narrow band gap of BiOI and a greatly effective separation of photoexcited carriers because of the built-in electric field on the interface between BiOI and Bi₂MoO₆. Moreover, the flower-like microstructure also promoted the adsorption of organic pollutants owing to the large surface area (about 10.36 m²/g), good for further photocatalytic degradation. As a result, BiOI/Bi₂MoO₆ p-n heterojunction showed an excellent photocatalytic activity of RhB of almost 95% in a short time of 90 min under wavelength longer than 420 nm, 2.3 and 2.7 times higher compared with single BiOI and Bi₂MoO₆, respectively. This work offers a promising approach to purify the environment through the utilization of solar energy by constructing efficient p-n junction photocatalysts.

Annealing and Plasma Effects on the Structural and Photocatalytic Properties of TiO2 Fibers Produced by Electrospinning

In this study, a combined method of heat treatment and plasma surface modification was used to improve the nanostructures and photocatalytic activity of electrospun TiO2 fibers. Based on the tuning effect of the annealing temperature from 500 to 800 °C, further improvements via the generation of H2 radiofrequency plasma reactions on the fiber’s surface were investigated. It was found that the anatase–rutile phase transition starts to occur at around 700 °C, which is higher than the common temperature for TiO2. The interfacial effect is generated by the symbiosis relationship between these two phases in the fibers, which can enhance photocatalytic activity since the anatase–rutile heterojunction in mixed-phase TiO2 is formed. The dramatic rise in oxygen vacancies on the fiber’s surface is created by the H2 plasma; this leads to the number of trapped electrons increasing and results in an accelerated separation between the photogenerated electrons and holes. Therefore, the photocatalytic mechanism, including the anatase–rutile heterojunction and the TiO2 fiber band structure containing oxygen vacancies, is predicted. The degradation rate was significantly enhanced (1.5 times) by increasing the annealing temperature up to 700 °C, which can be further improved upon after treatment with surface H2 plasma.

Improvement of Photocatalytic Performance by Building Multiple Heterojunction Structures of Anatase-Rutile/BiOI Composite Fibers

In this study, multiple heterojunction structures of anatase-rutile/Bismuth oxyiodide (BiOI) composite fibers are designed by the combined method of electrospinning and hydrothermal techniques. The influence of different Ti/Bi atomic ratios ([Ti/Bi]) on the nanostructures and photocatalytic properties are investigated. It is found that the morphology of BiOI covered on the TiO₂ fiber surface changed with [Ti/Bi] from nanosheets to submicron spheres structures. Additionally, the crystallization of the composite fibers including the phases of anatase, rutile, and BiOI is identified, theses phases are in close contact with each other, and the interfacial effects are helpful to form the multiple heterojunctions which lead to blue shifts on the chemical state of Ti. The absorption of visible light has been improved by compositing BiOI on TiO₂, while the band gap values of the composite fibers are significantly reduced, which can enhance the generation and separation of electrons and holes. For the case of [Ti/Bi] = 1.57, the photodegradation rate of anatase-rutile/BiOI composite fibers is about 12 times that of pure TiO₂. For the photocatalytic mechanism, the synergistic s-type heterojunctions increase the content of active oxides which have a positive effect on the degradation rate.

Role of p-n junction initiated mixed-dimensional 0D/2D, 1D/2D, and 2D/2D BiOX (X = Cl, Br, and I)/TiO2 nanocomposite interfaces for environmental remediation applications: A review

Nowadays, we are critically facing various environmental issues. Among these, water contamination is the foremost issue, which worsens our health and living organisms in the water. Thus, it is necessary to provide an avenue to minimize the toxic matter through the development of facile technique and harmless photocatalyst. In this review, we intended to uncover the findings associated with various 0D, 1D, and 2D nanostructures featured photocatalysts for advancements in interfacial characteristics and toxic matter degradation. In this context, we evaluated the promising mixed-dimensional 0D/2D, 1D/2D, and 2D/2D bismuth oxyhalides BiOX (X = Cl, Br, and I) integrated TiO₂ nanostructure interfaces. Tunable mixed-dimensional interfaces highlighted with higher surface area, more heterojunctions, variation in the conduction and valence band potential, narrowed band gap, and built-in electric field formation between BiOX and TiO₂, which exhibits remarkable toxic dye, heavy metals, and antibiotics degradation. Further, this review further examines insights into the charge carrier generation, separation, and shortened charge transfer path at reduced recombination. Considering the advantages of type-II, S-scheme, and Z-scheme charge transfer mechanisms in the BiOX/TiO₂, we heightened the combination of various reactive species generation. In a word, the concept of mixed-dimensional BiOX/TiO₂ heterojunction interface endows toxic matter adsorption and decomposition into useful products. Challenges and future perspectives are also provided.