Simple synthesis of BiOAc/BiOBr heterojunction composites for the efficient photocatalytic removal of organic pollutants

Photocatalytic removal of ammonia nitrogen from water: investigations and challenges for enhanced activity

Ammonia nitrogen (NH3-N/NH4+-N) serves as a crucial chemical in biochemistry and fertilizer synthesis. However, it is also a toxic compound, posing risks from eutrophication to direct threats to human health. Ammonia nitrogen pollution pervades water sources, presenting a significant challenge. While several water treatment technologies exist, biological treatment, though widely used, has its limitations. Hence, green and efficient photocatalytic technology emerges as a promising solution. However, current monolithic semiconductor photocatalysts prove inadequate in controlling ammonia nitrogen pollution. Therefore, this review focuses on enhancing semiconductor photocatalysts' efficiency through modification, discussing four mechanisms: (1) mono-ionic modification; (2) metallic and non-metallic modification; (3) construct heterojunctions; and (4) enhancement of synergistic effects of multiple technologies. The influencing factors of photocatalytic ammonia nitrogen removal efficiency are also explored. Moreover, the review outlines the limitations of current photocatalytic pollution treatment and discusses future development trends and research challenges. Currently, the main products of ammonia nitrogen removal include NO3-, NO2-, and N2. To mitigate secondary pollution, the green process of converting ammonia nitrogen to N2 using photocatalysis emerges as a fundamental approach for future treatment. Overall, this review aims to deepen understanding of photocatalysis in ammonia nitrogen treatment and guide researchers toward widespread implementation of this endeavor.

Porous Rod-like NiTiO3-BiOBr Heterojunctions with Highly Improved Visible-Light Photocatalytic Performance

NiTiO₃-BiOBr heterostructured photocatalysts were constructed via precipitation, calcination and hydrothermal treatments. Various characterizations demonstrated that BiOBr nanosheets were decorated on NiTiO₃ nanoparticals, forming porous rod-like heterojunctions. Compared with independent NiTiO₃ and BiOBr, the composites with optimal BiOBr content presented highly improved visible-light photocatalytic efficiency. The degradation rates of Rhodamine B (RhB) and tetracycline (TC) reached 96.6% in 1.5 h (100% in 2 h) and 73.5% in 3 h, which are 6.61 and 1.53 times those of NiTiO₃, respectively. The result is an improved photocatalytic behavior from the formation of heterojunctions with a large interface area, which significantly promoted the separation of photogenerated carriers and strengthened the visible-light absorption. Based on the free radical capture experiments and band position analysis, the photodegradation mechanism of type-II heterojunction was deduced. This study provides a new way to fabricate highly efficient NiTiO₃-based photocatalysts for degrading certain organics.

Construction of Z scheme S-g-C3N4/Bi5O7I photocatalysts for enhanced photocatalytic removal of Hg0 and carrier separation

Photocatalysis has demonstrated the potential to solve challenges in various practical application fields such as energy and environmental science due to its environmental friendliness. However, the photocatalytic activity is mainly affected by the weak absorption of visible light and the low separation efficiency of photogenerated carriers. Herein, an S-doped g-C₃N₄/Bi₅O₇I heterojunction was designed by the calcination method. It was found that S doping not only reduces the band gap of g-C₃N₄, which raises the optical absorption boundary of g-C₃N₄ from 465 nm to 550 nm. At the same time, the introduction of S elements leads to new doping energy levels, which can act as photogenerated electron trapping centers and thus inhibit the complexation of photogenerated carriers. Second, the construction of the heterojunction greatly facilitates the transport of carriers and the separation of electrons and holes driven by the built-in electric field. Finally, the abundant oxygen vacancies in the system result in defective energy levels that not only promote the activation of molecular oxygen, but also act as photogenerated electron traps, which further boost the separation of electron-hole pairs. Benefiting from the optimized performance, the photocatalytic reaction rates of S-doped g-C₃N₄/Bi₅O₇I are 5.2 and 2.1 times higher than those of g-C₃N₄ and Bi₅O₇I, respectively. This work provides a viable idea for the potential development of non-metal doping combined with heterojunction photocatalytic systems.

Construction of 3D sheet-packed hierarchical MoS2/BiOBr heterostructures with remarkably enhanced photocatalytic performance for tetracycline and levofloxacin degradation

In this paper, MoS₂ nanosheets were prepared and deposited on BiOBr microflowers through deposition-hydrothermal strategy. MoS₂ exhibited a string of nanosheets with wrinkled layer outlook, and MoS₂/BiOBr composites displayed a micro-flower morphology with the diameter of 2-3 μm. Visible-light harvesting performance was significantly improved in the region of 400-600 nm for MoS₂/BiOBr. The obtained MoS₂/BiOBr samples exhibited tremendous enhanced catalytic activity, which could degrade 92.96% of tetracycline and 90.31% of levofloxacin within 70 min. The photo-generated holes and ⋅OH radicals played the dominant roles in the whole photocatalytic decomposition process. Based on the analysis of DRS, BET, PL, and electrochemical results, the remarkably improved photocatalytic performance may be ascribed to the synergistic effect of strong visible-light harvesting ability, enhanced BET surface area, and faster separation or transfer efficiency of photo-generated charges.

Dye recovery with photoresponsive citric acid-modified BiOCOOH smart material: Simple synthesis, adsorption-desorption properties, and mechanisms

Dye recovery is of great significance for a circular economy and sustainable development. However, green recovery strategies without secondary pollution remain a significant challenge. To resolve this issue, a light-responsive smart material (citric acid-modified BiOCOOH (m-BOCH)) was synthesized and applied for dye recovery through adsorption in the dark, and desorption under visible light. With the modification of citric acid, the adsorption level of methylene blue (MB) on m-BOCH (43.4%) was more than six times that of pure BiOCOOH (7.1%). The desorption rate was ∼90% in 120 min under 420 nm light irradiation (there was no desorption for pure BOCH). Further, the adsorption rate was improved to 83.9% and the desorption rate remained stable at an optimal pH of 10.09. Characterization results indicated that carboxyl groups were modified onto the surface of BiOCOOH and served as adsorption sites for MB. Under visible light exposure, the connections between the carboxyl groups and BiOCOOH were damaged, which led to the desorption of MB from the surface of the m-BOCH. The recovered MB exhibited a good staining effect on hepatic stellate cells (HSC) as a fresh dye. The regeneration of m-BOCH was achieved through a moderate hydrothermal process, and the adsorption and desorption capacities were restored to 80.8% and 85.7%, respectively. This research provides a novel environmentally compatible strategy for dye recovery without secondary pollution. This is a very promising treatment technique for dye effluents, which highlights the application of smart materials resource recycling for environmental remediation.

In-situ construction of step-scheme MoS2/Bi4O5Br2 heterojunction with improved photocatalytic activity of Rhodamine B degradation and disinfection

In this paper, a novel Step-scheme MoS₂/Bi₄O₅Br₂ heterojunction was fabricated through the in-situ mechanical agitation method and the photocatalytic activity of that was examined by the photocatalytic degradation Rhodamine B (RhB) and inactivation of E.coli under visible light irradiation (λ > 420 nm). The Step-scheme MoS₂/Bi₄O₅Br₂ heterojunctions displayed the enhanced photocatalytic ability compared to pure Bi₄O₅Br₂ and MoS₂ and the MoS₂/Bi₄O₅Br₂-3% (MS/BOB-3) heterojunction exhibited the strongest photocatalytic activity which can completely inactivate the 1 × 10⁷ cfu/mL with 180 min and degrade RhB (10 mg/L) with 24 min visible light irradiation, respectively. The photocatalytic mechanism of the MoS₂/Bi₄O₅Br₂ heterojunction is was attributed to the generated active species (h⁺, ·O₂^- and ·OH) which can effectively destroy RhB molecular and cell-membrane of bacterial as demonstrated by multiple techniques such as LC-MS and fluorescence stain. Additionally, characterization results disclosed that the transfer pathway of charge carriers of constructed MoS₂/Bi₄O₅Br₂ heterojunction followed the Step-scheme channel, which not only facilitated the separation and migration of the photo-generated charge carriers, but also improved the light absorption ability of the samples and resulting in the promoted photocatalytic performance of MoS₂/Bi₄O₅Br₂ heterojunction. This work paves a new idea to develop novel bismuth oxyhalide-based photocatalytic system for wastewater purification.

Photocatalysis: an effective tool for photodegradation of dyes-a review

The disposal of dye-contaminated wastewater is a major concern around the world for which a variety of techniques are used for its treatment. The photocatalytic treatment of dye-contaminated wastewater is one of the treatment methods. Semiconductor-assisted photocatalytic treatment of dye-contaminated wastewater has gained pronounced attention recently. This review outlines the recent advancements in the photocatalytic treatment of dye-contaminated wastewater. The photocatalytic degradation of dyes follows three types of mechanisms: (1) dye sensitization through charge injection, (2) indirect dye degradation through oxidation/reduction, and (3) direct photolysis of dye. Several experimental parameters like initial concentration of dyes, pH, and catalyst dosage significantly affect the photocatalytic degradation of dyes. The photocatalytic materials can be categorized into three generations. The single-component (e.g., ZnO, TiO₂) and multiple component semiconductor metal oxides (e.g., ZnO-TiO₂, Bi₂O₃-ZnO) are categorized as first-generation and second-generation photocatalysts, respectively. The photocatalysts dispersed on an inert solid substrate (e.g., Ag-Al₂O₃, ZnO-C) are classified as third-generation photocatalysts. Finally, we reviewed the challenges that affect the photocatalytic degradation of dyes.