Visible-light photocatalytic activity enhancement of red phosphorus dispersed on the exfoliated kaolin for pollutant degradation and hydrogen evolution

CuInS2/Red Phosphorus Nanosheet Interleaved Heterostructures with Improved Interfacial Charge Transfer for Photoelectrochemical Aptasensing

Accelerating the migration of interfacial carriers in heterojunctions is crucial for achieving highly sensitive photoelectrochemical (PEC) sensing. In this study, we developed three-dimensional (3D)/two-dimensional (2D) CuInS2/red phosphorus nanosheet (CuInS2/RP NS) n-n heterojunction functional materials with enhanced interfacial charge transfer capabilities for PEC sensing. The 3D CuInS2 serves as a conductive layer, providing excellent electronic conductivity and superior electron absorption and transport properties. In contrast, the ultrathin RP NS acts as a transport layer that enhances carrier mobility. The 3D/2D heterojunction ensures a large interface contact surface, shortening the carrier transport distance. A well-aligned band position generates a substantial built-in electric field, providing a significant driving force for efficient carrier separation and migration, thereby improving response sensitivity. A PEC aptamer sensor was constructed based on the synthesized heterostructure for ciprofloxacin detection. The detection limit of the CuInS2/RP NS aptamer sensor for ciprofloxacin is 2.03 × 10-15 mg·mL-1, with a linear range from 1.0 × 10-14 to 1.0 × 10-5 mg·mL-1. This work presents a strategy for enhancing the photoelectric response by modulating the interface structure of heterojunctions, thereby opening new prospects for the application of highly sensitive PEC sensors in antibiotic detection.

Enhancing bacterial control and daylight-driven water remediation with chitosan-impregnated MoC nanosheets

The functionalization of nanoparticles with 2D nanosheets is an effective approach to enhance their functional properties for pollutant removal. This research outlines the synthesis of a 2D-delaminated molybdenum carbide (MXene) chitosan nanocomposite (2D-d-Mo2CTx-Cs NC) with bacterial control and photocatalytic properties for dye adsorption. The nanocomposite includes Tx-surface terminating groups O, OH, and F. In this investigation, the composite was synthesized using the etching method and its formation was confirmed through UV spectra at 288 nm. It was characterized through FTIR, XRD, Particle size, Zetapotential, FESEM, HRTEM, EDAX, and XPS analyses. FTIR spectral analysis of NC suggests that amines are formed through a Schiff base reaction between glutaraldehyde and Cs, or through the interaction of terminal aldehydes and carbonyl groups. The XRD analysis confirmed the crystalline structure of the composite. FESEM images revealed irregularly structured nanosheets (NSs) material in the prepared 2D-d-Mo2CTx-Cs NC samples. HRTEM images revealed 2D-d-Mo2CTx NSs impregnated onto Cs with an average size of 50 nm, as confirmed by a particle size analyzer, with a zeta potential value of - 15 mV. Additionally, Mo, C, N, and O are the most significant elements present in the NC, as confirmed by EDAX and XPS analyses. Further, biocompatibility testing of 2D-d-Mo2CTx-Cs NC yielded positive results. Moreover, under sunlight, the composites effectively adsorbed methylene blue with a 90% adsorption capacity, as confirmed by kinetic studies. Furthermore, the synergistic effect of Cs and d-Mo2CTx NSs resulted in significant antibacterial (50-200 µl of 1 mg/ml) and antibiofilm activity (100 µl of 1 mg/ml) against pathogenic bacteria. Furthermore, this study represents the first report on the use of 2D-d-Mo2CTx-Cs NC for daylight-influenced photocatalytic applications with a bacteria-controlling effect.

Visible light photocatalysis: efficient Z-scheme LaFeO3/g-C3N4/ZnO photocatalyst for phenol degradation

In this work, a Z-scheme LaFeO3/g-C3N4/ZnO heterojunction photocatalyst with large specific surface (68.758 m2/g) and low cost (0.00035 times the cost of per gram of Au) was easily synthesized by glucose-assisted hydrothermal method. The structure, surface morphology, and optical properties of the photocatalyst were investigated. The constructed Z-scheme heterojunction catalysts can enhance the visible light absorption and carrier separation efficiency. Among these photocatalysts, the 10%-LaFeO3/g-C3N4/ZnO composite possesses the premium performance for efficient degrading 97.43% of phenol within 120 min. Even after 5 cycles, it still sustains an excellent photocatalytic stability (92.13% phenol degradation). According to the XPS surface states and the capture of active species on LaFeO3/g-C3N4/ZnO, the electrons would be transferred from ZnO and LaFeO3 to g-C3N4. In addition, ·OH plays an important role in photocatalytic reactions for phenol degradation. Thus, the proposed possible photocatalytic reaction mechanism of Z-scheme LaFeO3/g-C3N4/ZnO can provide a more economical and efficient conception for phenol degradation.

Efficient photodegradation of PFOA using spherical BiOBr modified TiO2 via hole-remained oxidation mechanism

Photo-induced holes (h⁺) oxidation is an efficient approach for perfluorooctanoic acid (PFOA; C₇F₁₅COOH) removal. To maintain a high amount of h⁺ on the surface of photocatalysts participating in the PFOA photodegradation could be a critical issue. Herein, a highly efficient spherical BiOBr-modified nano-TiO₂ (P25) was synthesised and used for PFOA photodegradation through direct oxidation with h⁺. A high number of h⁺ could be generated and remain on the surface of P25/BiOBr due to the appropriate position of the conduction band (CB) and valence band (VB) levels between P25 and BiOBr. Meanwhile, PFOA molecules were coordinated to the P25/BiOBr's surface via unidentate binding, being directly activated and oxidised by h⁺, resulting in a decomposition yield of 99.5% (100 mg/L) under simulated solar light irradiation within 100 min, at the initial pH condition (3.5). A stepwise photodegradation pathway was proposed due to the significant intermediates detected as the short-chain perfluorinated carboxylic acids (C2-C7). Reactive oxygen species (ROS) generation, scavenging and trapping analysis indicated that the direct oxidation on h⁺ followed PFOA degradation. In a real aqueous environment of Tangxun lake (adjusted pH 3.5), stable common anions and natural organic matter (NOM) would restrain the PFOA photodegradation. However, adding 10 mg/L of NO₃^- or HA could reduce the inhibition effect of PFOA photodegradation. These findings gave an alternative strategy to drive an h⁺ directly oxidation to treat PFOA contaminated water bodies.

Enhanced photocatalytic and antibacterial activities of S-scheme SnO2/Red phosphorus photocatalyst under visible light

The construction of wide bandgap semiconductors with heterojunctions is an effective strategy to improve the photocatalytic activity of narrow-bandgap semiconductors, such as red phosphorus (RP). The novel step-scheme (S-scheme) heterojunction can separate photocarriers effectively while retaining the high reduction-oxidation capacity of the catalyst. Herein, a SnO₂/hydrothermally treated RP (SnO₂/HRP) S-scheme heterojunction was constructed and was found to display superior performance in the photocatalytic degradation of pollutants and the disinfection of bacteria. The 5%SnO₂/HRP (mass ration of SnO₂ with 5 wt%) composite had the strongest photocatalytic activity. It could degrade 97.5% of Rhodamine B (RhB) after 12 min of light exposure. The photodegradation rate constant of this composite reached 2.96 × 10^-1 min^-1, which was 4.4 and 59.2 times higher than that of pure HRP and SnO₂, respectively. Furthermore, this S-scheme heterojunction composite exhibited a higher efficient photocatalytic antibacterial rate (99.4%) for Escherichia coli (E. coli) under visible-light irradiation, than pure HRP (66.4%) and SnO₂ (72.9%). Further mechanistic investigations illustrated that the intimate contact between HRP and SnO₂ in the S-scheme system heterojunction could effectively boost carrier transfer and improve the photocatalytic activity of the semiconductor. This investigation provided an efficient recyclable S-scheme heterojunction composite for the photocatalytic degradation of pollutants and bacteria.

Broad Spectral Response Z-Scheme Three-Dimensional Ordered Macroporous Carbon Quantum Dots/TiO2/g-C3N4 Composite for Boosting Photocatalysis

Photocatalytic degradation technology is one of the effective protocols to solve environmental problems. TiO₂ has always been favored for its photostability and low cost. However, the insufficient photocatalytic activity of TiO₂ limits its application due to the severe recombination of photogenerated electrons and holes and a narrow light response range. Therefore, 3DTCN, a TiO₂/g-C₃N₄ composite with a three-dimensional ordered macroporous structure was prepared by a colloidal crystal template technique to form a heterojunction for inhibiting the photogenerated electron-hole recombination. On 3DTCN, carbon quantum dots (CQDs) were loaded by impregnation to obtain x % CQDs/3DTCN with a broad spectral response to light. The physical and chemical properties of samples were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution-TEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller analysis, photoluminescence spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy. The photocatalytic activity was evaluated via degrading the rhodamine B (RhB) dye, and the degradation efficiency of 1% CQDs/3DTCN (98%) was found to be much higher than that of 3DTCN (42%) in 80 min under simulated sunlight irradiation. Furthermore, it also possessed excellent durability. Meanwhile, the sample also showed an outstanding photoelectric property. Finally, the proposed mechanism of the composites had been mainly analyzed by density functional theory calculations. This work thus provides an idea to form a 3D structure heterojunction and further improve the photocatalytic activity.

Red Phosphorus: An Up-and-Coming Photocatalyst on the Horizon for Sustainable Energy Development and Environmental Remediation

Photocatalysis is a perennial solution that promises to resolve deep-rooted challenges related to environmental pollution and energy deficit through harvesting the inexhaustible and renewable solar energy. To date, a cornucopia of photocatalytic materials has been investigated with the research wave presently steered by the development of novel, affordable, and effective metal-free semiconductors with fascinating physicochemical and semiconducting characteristics. Coincidentally, the recently emerged red phosphorus (RP) semiconductor finds itself fitting perfectly into this category ascribed to its earth abundant, low-cost, and metal-free nature. More notably, the renowned red allotrope of the phosphorus family is spectacularly bestowed with strengthened optical absorption features, propitious electronic band configuration, and ease of functionalization and modification as well as high stability. Comprehensively detailing RP's roles and implications in photocatalysis, this review article will first include information on different RP allotropes and their chemical structures, followed by the meticulous scrutiny of their physicochemical and semiconducting properties such as electronic band structure, optical absorption features, and charge carrier dynamics. Besides that, state-of-the-art synthesis strategies for developing various RP allotropes and RP-based photocatalytic systems will also be outlined. In addition, modification or functionalization of RP with other semiconductors for promoting effective photocatalytic applications will be discussed to assess its versatility and feasibility as a high-performing photocatalytic system. Lastly, the challenges facing RP photocatalysts and future research directions will be included to propel the feasible development of RP-based systems with considerably augmented photocatalytic efficiency. This review article aspires to facilitate the rational development of multifunctional RP-based photocatalytic systems by widening the cognizance of rational engineering as well as to fine-tune the electronic, optical, and charge carrier properties of RP.

Bi2O2CO3/red phosphorus S-scheme heterojunction for H2 evolution and Cr(VI) reduction

Red phosphorus (RP) has a suitable energy band structure and excellent photocatalytic properties. However, there are some problems, such as low quantum efficiency and serious photogenerated electron-hole recombination. The S-scheme heterostructure shows great potential in facilitating the separation and transfer of photogenerated carriers and obtaining strong photo-redox ability. Herein, hydrothermally treated red phosphorus (HRP) was combined with Bi₂O₂CO₃ to construct Bi₂O₂CO₃/HRP S-scheme heterojunction composite. The Bi₂O₂CO₃ content was optimized, and the 5 %Bi₂O₂CO₃/HRP composite obtained at 5 %Bi₂O₂CO₃ mass fraction exhibited the strongest photoreduction ability. The Cr(VI) photoreduction and photolytic hydrogen production rates were as high as 0.22 min^-1 and 157.2 μmol •h^-1, which were 7.3 and 3.0 times higher than those of HRP, respectively. The promoted photocatalytic activity could be attributed to the formation of S-scheme heterojunctions, which accelerated the separation and transfer of useful photogenerated electron-hole pairs, while enhancing the recombination of relatively useless photogenerated electron-hole pairs, thereby resulting in the highest photocurrent density (17.3 μA/cm²) of the 5 %Bi₂O₂CO₃/HRP composite, which was 1.6 and 4.3 times higher than pure Bi₂O₂CO₃ (10.5 μA/cm²) and pure HRP (4.0 μA/cm²), respectively. This work would provide an advanced approach to enhance the photocatalytic activity of RP.

Constructing a Z-scheme ZnIn2S4-S/CNTs/RP nanocomposite with modulated energy band alignment for enhanced photocatalytic hydrogen evolution

Energy band structures greatly determine the charge separation and transfer properties in heterojunction photocatalysts and consequently their photocatalytic activities. Herein, a well-designed Z-scheme ZnIn₂S₄-S/CNTs/RP (ZIS-S/CNTs/RP) nanocomposite was fabricated according to an energy band alignment steering strategy to realize superior photocatalytic H₂ evolution performance. The ZIS-S/CNTs/RP nanocomposite shows an efficient photocatalytic H₂ evolution rate of 1639.9 μmol g^-1h^-1, which is noticeably higher than that of pristine red phosphorus (RP) and CNTs/RP and ZIS-S/RP composites, as well as those of the compared heterojunctions using bulk RP or ZnIn₂S₄. Owing to the modification of nanosized RP and the introduction of sulfur vacancies in ZnIn₂S₄, a tailored energy band alignment of the heterojunction with a higher reduction potential and larger Fermi level potential difference was achieved, which resulted in significantly increased photogenerated electron-hole separation efficiency and a more efficient Z-scheme charge transfer mechanism, thus promoting the photocatalytic activity of ZIS-S/CNTs/RP. This work aims to provide a novel effective strategy for the construction of high-performance heterojunction photocatalysts by energy band engineering.

Novel S-scheme RP/NiCo-LDH composite with remarkably enhanced photocatalytic activity for H2 evolution under visible-light irradiation

A novel red phosphorus/nickel cobalt layered double hydroxide (RP/NiCo-LDH) heterojunction was successfully prepared and exhibited an excellent photocatalytic performance for hydrogen evolution.