A critical review on bismuth oxyhalide based photocatalysis for pharmaceutical active compounds degradation: Modifications, reactive sites, and challenges

Pharmaceutical active compounds (PhACs), as a kind of widely used pharmaceutical drugs, has attracted much attention. The bismuth oxyhalides (BiOX)-based photocatalysis can remove PhACs efficiently due to its unique layered structure, optical and electronic properties. Nevertheless, the rapid recombination of photogenerated electron-hole pairs, and the inherent instability of structure have limited its practical application. In order to solve these problems, recent modification studies tend to focus on facet control, elemental doping, bismuth-rich strategies, defect engineering and heterojunction. Therefore, the objective of this review is to summarize the recent developments in multiply modified strategies for PhACs degradation. The synthesis methods, photocatalytic properties and the enhancement mechanism are elaborated. Besides, based on theoretical calculation, the reactive sites of typical PhACs attacked by different reactive oxygen species were also proposed. Subsequently, challenges and opportunities in applications are also featured which include factors, viz., dissolution of halogen ions, instability under visible light, applications of real water/wastewater, intermediates and byproducts toxicity analysis of BiOX-based photocatalysis. Finally, the perspectives of BiOX-based photocatalysis for PhACs photodegradation in actual water applications are highlighted.

Electronic Structures and Lattice Dynamics of Layered BiOCl Single Crystals

BiOCl has recently elicited intense interest for its excellent photochemical catalysis, energy conversion, and photodetection performance. In this Letter, we systematically investigate BiOCl electronic properties, lattice dynamics, and structural stability. From first-principles calculations, bulk and monolayer BiOCl have ultraviolet indirect band gaps around 3.6 eV, consistent with reflection spectroscopy measurements. The large spin-orbit coupling effect of the Bi atom makes the lowest conduction band near the Z point in the Brillouin region move down 230 meV. However, because of the symmetrical crystal potential, BiOCl has no strong Rashba effect. We further observed all 6 BiOCl Raman-active modes with the lowest-frequency rigid layer in-plane vibrational mode at 63 cm^-1, consistent with our calculations. Up to 500 K or down to monolayer thickness, the crystal structure of BiOCl remains stable. Our work provides detailed information on BiOCl electronic and vibrational properties and stability up to high temperature or down to monolayer, identifying it as a promising layered material for further nano-optoelectronic applications.

Novel Bi3O5I2 Hollow Microsphere and Its Enhanced Photocatalytic Activity

A new type of I-deficient bismuth oxyiodide Bi3O5I2 with a hollow morphology was prepared by the solvothermal process. The structure, composition, morphology, optical property and photoelectric property of the as prepared photocatalyst were investigated through some characterization methods. Those characterization results showed that Bi3O5I2 displayed a larger specific surface area, promising band structure and lower recombination of photoinduced carriers than pure BiOI. Bi3O5I2 had a higher photocatalytic activity than BiOI on the decomposition of methyl orange (MO) under simulated solar light irradiation. The superoxide (·O2−) and hole (h+) were the dominating active species during the degradation of MO. Its stability and reusability performance showed its great promising application in the degradation of organic pollutant.

Strong Hollow Spherical La2NiO4 Photocatalytic Microreactor for Round-the-Clock Environmental Remediation

This work reports a moderate round-the-clock route to treating organic pollutants by utilizing a La₂NiO₄ hollow-sphere microreactor. A glycerol-assisted solvothermal route followed by an annealing process was applied for fabricating the catalyst. Both the physicochemical properties and the catalytic performance of the as-obtained microreactor for treating pollutants were discussed. The microreactor exhibited a strong ability to degrade phenol and anionic dyes in the absence of light irradiation, owing to its high surface area and positively charged surface. With the aid of visible-light irradiation, the degradation rate of the organic pollutants could be further accelerated due to the light multireflection in a hollow structure, which enhances the utilization of light. The present work indicates that the hollow-sphere La₂NiO₄ microreactor is effectively energy saving for environmental remediation.

Surfactant free fabrication and improved charge carrier separation induced enhanced photocatalytic activity of {001} facet exposed unique octagonal BiOCl nanosheets

Unique octagonal shaped BiOCl nanosheets (NS) dominantly exposed with high energy {001} crystal facets have been fabricated via a simple hydrothermal route without using organic surfactants. The dynamics of photogenerated charge carriers have been studied by time-resolved photoluminescence spectroscopy. The fitting parameters of the decay kinetics were used to calculate both the intensity weighted average lifetime (〈τ〉int.), as well as the amplitude weighted average lifetime (〈τ〉amp.) of the photogenerated charge carriers. The 〈τ〉int. and 〈τ〉amp. values for {001} BiOCl NS, i.e., 17.23 ns and 1.94 ns, respectively, were observed to be significantly higher than the corresponding values obtained for pristine BiOCl such as 2.52 ns and 1.07 ns, respectively. Significant quenching of the PL emission intensity of {001} BiOCl NS reflected the enhanced separation of the photogenerated charge carriers. Reduced thickness and in situ iodine doping was favorable to minimize the recombination tendency. The photocatalytic activity was monitored via the photodegradation of RhB under visible light illumination (λ > 400 nm). {001} BiOCl NS exhibited superior performance when compared to pristine BiOCl in terms of the rapid degradation kinetics and higher photonic efficiency. The photocatalytic efficiency of {001} BiOCl NS was 2.8 times higher than pristine BiOCl. Iodine doping induced extended the optical absorption in the visible region and improved the separation of the photogenerated charge carriers, which played an important role to enhance the photocatalytic activity. The photodegradation mechanism was systematically studied using various radical quenchers and it was revealed that photogenerated holes (h(+)) and superoxide radicals (˙O(2-)) actively participated whereas hydroxyl (OH˙) radicals had a negligible contribution in the photodegradation of RhB. {001} BiOCl NS has shown a higher photocurrent density and lower charge transfer resistance analyzed through photoelectrochemical and electrochemical impedance measurements. This study highlights the fabrication of unique octagonal BiOCl NS with improved separation of charge carriers across high energy crystal facts to design a highly efficient photocatalyst.

Multiple halide anion doped layered bismuth terephthalate with excellent photocatalysis for pollutant removal

Doping multiple halide anions into bismuth terephthalate can effectively improve photocatalytic activities. The F^–, Cl^–, Br^– codoped hybrids exhibit excellent photocatalytic activities on RhB and salicylic acid.

Remarkable promoting effects of BiOCl on the room-temperature selective oxidation of benzyl alcohol over supported Pt catalysts

BiOCl, in addition to traditional Bi metal, could remarkably promote the catalytic performance of Pt/MO_x in the selective oxidation of benzyl alcohol.

Core-shell nanoparticles: synthesis and applications in catalysis and electrocatalysis

Core-shell nanoparticles (CSNs) are a class of nanostructured materials that have recently received increased attention owing to their interesting properties and broad range of applications in catalysis, biology, materials chemistry and sensors. By rationally tuning the cores as well as the shells of such materials, a range of core-shell nanoparticles can be produced with tailorable properties that can play important roles in various catalytic processes and offer sustainable solutions to current energy problems. Various synthetic methods for preparing different classes of CSNs, including the Stöber method, solvothermal method, one-pot synthetic method involving surfactants, etc., are briefly mentioned here. The roles of various classes of CSNs are exemplified for both catalytic and electrocatalytic applications, including oxidation, reduction, coupling reactions, etc.

Tunable photocatalytic and photoelectric properties of I−-doped BiOBr photocatalyst: dramatic pH effect

Dramatic effect of synthesis pH was discovered for expediently tuning photocatalytic and photoelectric properties of I⁻-doped BiOBr photocatalyst.

The photocatalytic properties of ultrathin bismuth oxychloride nanosheets: a first principles study

The built-in electric field can promote the separation of photo-generated carriers in the ultrathin BiOCl(001) nanosheet.

BiOCl/SnS2 hollow spheres for the photocatalytic degradation of waste water

A kind of novel SnS₂-incorporated BiOCl hollow spheres are synthesized. The band structure tuning effect and the morphological benefits of the hollow sphere structure greatly improved the performance in photocatalysis.

Facile synthesis of Ag/AgCl/BiPO4 plasmonic photocatalyst with significantly enhanced visible photocatalytic activity and high stability

Highly efficient Ag/AgCl/BiPO₄ plasmonic photocatalyst was synthesized for the first time. The catalyst showed excellent visible photocatalytic activity and high stability. A surface plasmon resonance mechanism was investigated.

Bismuth oxyhalide nanomaterials: layered structures meet photocatalysis

In recent years, layered bismuth oxyhalide nanomaterials have received more and more interest as promising photocatalysts because their unique layered structures endow them with fascinating physicochemical properties; thus, they have great potential photocatalytic applications for environment remediation and energy harvesting. In this article, we explore the synthesis strategies and growth mechanisms of layered bismuth oxyhalide nanomaterials, and propose design principles of tailoring a layered configuration to control the nanoarchitectures for high efficient photocatalysis. Subsequently, we focus on their layered structure dependent properties, including pH-related crystal facet exposure and phase transformation, facet-dependent photoactivity and molecular oxygen activation pathways, so as to clarify the origin of the layered structure dependent photoreactivity. Furthermore, we summarize various strategies for modulating the composition and arrangement of layered structures to enhance the photoactivity of nanostructured bismuth oxyhalides via internal electric field tuning, dehalogenation effect, surface functionalization, doping, plasmon modification, and heterojunction construction, which may offer efficient guidance for the design and construction of high-performance bismuth oxyhalide-based photocatalysis systems. Finally, we highlight some crucial issues in engineering the layered-structure mediated properties of bismuth oxyhalide photocatalysts and provide tentative suggestions for future research on increasing their photocatalytic performance.

Engineering BiOX (X = Cl, Br, I) nanostructures for highly efficient photocatalytic applications

Heterogeneous photocatalysis that employs photo-excited semiconductor materials to reduce water and oxidize toxic pollutants upon solar light irradiation holds great prospects for renewable energy substitutes and environmental protection. To utilize solar light effectively, the quest for highly active photocatalysts working under visible light has always been the research focus. Layered BiOX (X = Cl, Br, I) are a kind of newly exploited efficient photocatalysts, and their light response can be tuned from UV to visible light range. The properties of semiconductors are dependent on their morphologies and compositions as well as structures, and this also offers the guidelines for design of highly-efficient photocatalysts. In this review, recent advances and emerging strategies in tailoring BiOX (X = Cl, Br, I) nanostructures to boost their photocatalytic properties are surveyed.

A highly efficient visible-light driven photocatalyst: two dimensional square-like bismuth oxyiodine nanosheets

2D square-like BiOI thin nanosheets with exposure of {001} facets present highly efficient visible-light photocatalytic performance.

One-pot solvothermal synthesis of singly doped Eu3+ and codoped Er3+, Yb3+ heavy rare earth oxysulfide Y2O2S nano-aggregates and their luminescence study

Highly crystallized micro/nano-sized Y₂O₂S were prepared through a one-pot mild solvothermal synthesis. By simply adjusting the amount of initial sulfur powder, the morphology and assembled structures can be well controlled.