Evaluation of practical application potential of a photocatalyst: Ultimate apparent photocatalytic activity

Harnessing Solar Energy for the Photocatalytic Reduction of Hexavalent Chromium: A High-Performance Yarrowia lipolytica-CdS Biohybrid System

Photosynthetic semiconductor biohybrids, which combine the light-harvesting capacity of semiconductors and catalytic activity of whole-cell microorganisms, show substantial potential for advancing bioremediation technology. However, few yeast-based biohybrid systems for pollutant removal were reported. In this study, we have constructed a whole-cell biohybrid system based on Yarrowia lipolytica featuring in situ synthesized biocompatible cadmium sulfide (CdS) nanoparticles (NPs) for the photocatalytic reduction of hexavalent chromium [Cr(VI)] under UV irradiation. The integration of these CdS NPs onto the surface of modified Y. lipolytica cells endowed the system with excellent photocatalytic performance, achieving 100% Cr(VI) reduction within 2 h. The system exhibited a higher kinetic constant (0.03 min-1). In the trapping experiments, the reactive oxygen species (ROS) generated photochemically, specifically the superoxide anion (•O2-), which were identified as crucial mediators that facilitate the reduction of Cr(VI). The enhanced activity of the Y. lipolytica-CdS biohybrid was attributed to efficient electron transfer. Additionally, through transcriptome analysis, we found that the differentially expressed genes are associated with membrane transport, oxidation-reduction process, energy metabolism, and electron transfer. This whole-cell biohybrid catalytic strategy holds promise as an innovative approach for the reduction of Cr(VI) and has the potential to enhance our understanding of the interactions among light, inorganic material, and microorganisms.

In situ fabricated gold nanostars on hydrogel beads as photo-oxidase mimics for rapid and sustainable POCT of uric acid

Synthetic enzyme mimics surpass their natural counterparts in terms of stability, efficiency, and cost-effectiveness, making them highly valuable for catalytic applications. Gold nanomaterials, particularly gold nanostars, have emerged as promising enzyme mimetic nanocatalysts due to their enhanced light interaction and superior catalytic efficiency. In this study, gold nanostars grown in situ on the surface of core-shell hydrogel beads exhibited specific oxidase-like activity when exposed to light. Photoexcitation of gold nanostars generates singlet oxygen through the interaction of positive holes and superoxide radicals, resulting in photo-oxidase-like activity. Attaching the gold nanostars to the hydrogel bead surface prevented catalytic activity loss caused by agglomeration, resulting in a marked improvement in catalytic stability. This stability is evident from the sustained catalytic activity of the hydrogel bead-embedded gold nanostars, even after 60 days of prolonged incubation in an aqueous medium, and their strong catalytic performance across multiple reaction cycles. Leveraging this photo-oxidase-like activity, a point-of-care testing (POCT) setup is developed for highly sensitive uric acid detection. The system achieved a remarkable detection limit of 0.9 μM and demonstrated excellent accuracy in blood serum and urine sample analyses. Furthermore, the integration of smartphone technology facilitated rapid and convenient on-site testing, bridging the gap between laboratory settings and real-world applications. This approach offers a practical and sustainable solution for efficient and accurate uric acid monitoring in diverse settings.

Metal-organic framework heterojunctions for photocatalysis

Heterojunctions combining two photocatalysts of staggered conduction and valence band energy levels can increase the photocatalytic efficiency compared to their individual components. This activity enhancement is due to the minimization of undesirable charge recombination by the occurrence of carrier migration through the heterojunction interface with separated electrons and holes on the reducing and oxidizing junction component, respectively. Metal-organic frameworks (MOFs) are currently among the most researched photocatalysts due to their tunable light absorption, facile charge separation, large surface area and porosity. The present review summarizes the current state-of-the-art in MOF-based heterojunctions, providing critical comments on the construction of these heterostructures. Besides including examples showing the better performance of MOF heterojunctions for three important photocatalytic processes, such as hydrogen evolution reaction, CO2 photoreduction and dye decolorization, the focus of this review is on describing synthetic procedures to form heterojunctions with MOFs and on discussing the experimental techniques that provide evidence for the operation of charge migration between the MOF and the other component. Special attention has been paid to the design of rational MOF heterojunctions with small particle size and controlled morphology for an appropriate interfacial contact. The final section summarizes the achievements of the field and provides our views on future developments.

Nano spinel NiAl2O4: structure, optical and photocatalytic performance evaluation and optimization

Four kinds of spinel NiAl2O4were synthesized by the polyacrylamide gel method using Al2(SO4)3·18H2O and Al(NO3)3·9H2O as aluminum salts and anhydrous NiSO4and NiSO4·6H2O as nickel salts. The effects of different aluminum salts and nickel salts on the structure, optical and photocatalytic activity of spinel NiAl2O4were confirmed by various characterizations. There is no NiO impurity in the spinel NiAl2O4synthesized with Al2(SO4)3·18H2O as aluminum salt, while NiAl2O4, NiO and C-O functional group coexist in the target product with Al(NO3)3·9H2O as aluminum salt, and C-O functional group and NiO inhibits the photocatalytic activity of the system. Based on photocatalytic experiment, response surface methodology and free radical verification experiment, the influence of experimental parameters including synthesis pathway, initial drug concentration, initialpHand catalyst content on the photocatalytic activity of spinel NiAl2O4and the main active species involved in the reaction were investigated. The degradation percentage of spinel NiAl2O4synthesized with Al2(SO4)3·18H2O as aluminum salt and NiSO4·6H2O as nickel salt was 86.3% at the initial concentration of 50 mg l-1,pH= 5.33 and catalyst content of 1 g l-1. The mechanism investigation confirmed that the C-O functional group plays the dual role of impurity level and electron transfer in the degradation of tetracycline hydrochloride by spinel NiAl2O4.

Efficient photodegradation of polystyrene microplastics integrated with hydrogen evolution: Uncovering degradation pathways

Photocatalytic microplastics (MPs) conversion into valuable products is a promising approach to alleviate MPs pollution in aquatic environments. Herein, we developed an amorphous alloy/photocatalyst composite (FeB/TiO₂) that can successfully convert polystyrene (PS) MPs to clean H₂ fuel and valuable organic compounds (92.3% particle size reduction of PS-MPs and 103.5 μmol H₂ production in 12 h). FeB effectively enhanced the light-absorption and carrier separation of TiO₂, thereby promoting more reactive oxygen species generation (especially ‧OH) and combination of photoelectrons with protons. The main products (e.g., benzaldehyde, benzoic acid, etc.) were identified. Additionally, the dominant PS-MPs photoconversion pathway was elucidated based on density functional theory calculations, by which the significant role of ‧OH was demonstrated in combination with radical quenching data. This study provides a prospective approach to mitigate MPs pollution in aquatic environments and reveals the synergistic mechanism governing the photocatalytic conversion of MPs and generation of H₂ fuel.

The optimized Fenton-like activity of Fe single-atom sites by Fe atomic clusters-mediated electronic configuration modulation

The performance optimization of isolated atomically dispersed metal active sites is critical but challenging. Here, TiO2@Fe species-N-C catalysts with Fe atomic clusters (ACs) and satellite Fe-N4 active sites were fabricated to initiate peroxymonosulfate (PMS) oxidation reaction. The AC-induced charge redistribution of single atoms (SAs) was verified, thus strengthening the interaction between SAs and PMS. In detail, the incorporation of ACs optimized the HSO5- oxidation and SO5·- desorption steps, accelerating the reaction progress. As a result, the Vis/TiFeAS/PMS system rapidly eliminated 90.81% of 45 mg/L tetracycline (TC) in 10 min. The reaction process characterization suggested that PMS as an electron donor would transfer electron to Fe species in TiFeAS, generating 1O2. Subsequently, the hVB+ can induce the generation of electron-deficient Fe species, promoting the reaction circulation. This work provides a strategy to construct catalysts with multiple atom assembly-enabled composite active sites for high-efficiency PMS-based advanced oxidation processes (AOPs).

Efficient electro-catalyzed PMS activation on a Fe-ZIF-8 based BTNAs/Ti anode: An in-depth investigation on anodic catalytic behavior

Phenanthrene (PHE), mainly released from coal tar and petroleum distillation, is an important kind of prevalent polycyclic aromatic hydrocarbons (PAHs) contamination in China (up to 2.38 ± 0.02 mg/kg in soil and 8668 ng/L in surface water) and other countries in the world. Metal-organic frameworks (MOFs) show promising application prospects in the decontamination field, however, suffering from the intrinsic fragility and fine powder forms. Therefore, macroscopic MOFs architecture-sandwich-like Fe-ZIF-8/blue TiO₂ nanotube arrays (BTNAs)/Ti substrate (FBTT) anode with strong interfacial bonding (Fe-O-Ti and Fe-2-MIM-Ti coordination) was constructed using innovative in situ growth, condensation-crystallization-deposition, and pyrolysis methods, aiming at exploring the feasibility of MOFs-based anode/peroxymonosulfate (PMS) mediated PHE elimination, revealing the in-depth mechanisms, simultaneously overcoming the intrinsic drawbacks of MOFs. The FBTT-4 (doping content of 30 %) efficiently degraded PHE by 90.01 % and 74.5 % within 10 min at 350 μg/L and 3 mg/L, respectively, mediated by the ^·OH compared to the SO₄^·-, ¹O₂, and O₂^·-. Post-optimized range of anodic potential enabled (i) anodic oxidation, (ii) activation of water and PMS molecules to produce active species, (iii) capture of electrons in reactants to reduce Fe³⁺/Ti⁴⁺ to Fe²⁺/Ti³⁺, maintaining the proportion of Fe/Ti with low valence and thus stable PMS activation capacity, and (iv) regulation of the Fe/Ti d-band center to modulate the anode adsorption capacity. The further increment in anodic potential could promote "dark photocatalysis" with a Z-scheme-like mechanism. Thus, it is proposed that the development of macroscopic MOFs-based anode, especially those with small band gaps, represents vast potentials in electrocatalytic contamination elimination. Simultaneously, the MOFs-based anode is expected to fully exploit their catalytic capacities and solve their intrinsic defects as well.

Characterization Methodology and Activity Evaluation of Solar-Driven Catalysts for Environmental Remediation

Solar-driven photocatalysis mediated by semiconductors has been rapidly developed as a green and sustainable technology for environmental remediation. Continuous efforts have been devoted to novel semiconducting photocatalysts to boost the efficiency of the photocatalytic system. However, controversy has widely existed in materials characterization and photocatalytic activity evaluation. This review overviews the recent advances in characterization methodology and photocatalytic activity evaluation of solar-driven catalysts (SDCs) for environmental remediation. After a general and brief introduction of different SDCs, the compositional, structural, and optical characterizations of SDCs are summarized. Moreover, the characterization methods and challenges in the doped and coupled SDCs are discussed. Finally, the challenges in the evaluation of current evaluation methods for the photocatalytic activity of SDCs are highlighted.

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.