Highly dispersed BiOCl decahedra with a highly exposed (001) facet and exceptional photocatalytic performance

Ferroelectric Polarization and Iron Substitution Synergistically Boost Electrocatalytic Oxygen Evolution Reaction in Bismuth Oxychloride Nanosheets

Ferroelectric materials have gained significant interest in various kinds of water splitting, but the study of ferroelectric materials for electrocatalytic water splitting is in its infancy. Ferroelectric materials have spontaneous polarization below their Curie temperature due to dipolar alignment, which results in surface charges. In 2D ferroelectric materials, spontaneous polarization depends on thickness. Herein, we report that thickness-dependent ferroelectric polarization in 2D nanosheets can also accelerate the oxygen evolution reaction (OER) along with the tailored active surface area of exposed crystalline facets, which improves the electrocatalytic activity relatively. Iron-substituted BiOCl nanosheets of varying thickness are fabricated by varying the pH using a facile coprecipitation method. The substituted iron enhances polarization and electrochemical active sites on the surface. The findings in this study show that the exposed (001) facet and higher thickness of the nanosheets have high ferroelectric polarization and, in turn, superior electrocatalytic activity and remarkable stability, requiring low overpotentials (348 mV and 270 mV at 100 mA/cm2 and 10 mA/cm2) in alkaline (1.0 M KOH) electrolyte. As the thickness of the nanosheets is decreased from 140 to 34 nm, the electrocatalytic performance of iron-substituted BiOCl nanosheets starts to reduce due to the lower Coulomb-Coulomb interaction and the increasing depolarization.

Chelated Ion-Exchange Strategy toward BiOCl Mesoporous Single-Crystalline Nanosheets for Boosting Photocatalytic Selective Aromatic Alcohols Oxidation

The photoresponse and photocatalytic efficiency of bismuth oxychloride (BiOCl) are greatly limited by rapid recombination of photogenerated carriers. The construction of porous single-crystal BiOCl photocatalyst can effectively alleviate this issue and provide accessible active sites. Herein, a facile chelated ion-exchange strategy is developed to synthesize BiOCl mesoporous single-crystalline nanosheets (BiOCl MSCN) using acetic acid and ammonia solution respectively as chelating agent and ionization promoter. The strong chelation between acetate ions and Bi³⁺ ions introduces acetate ions into the precipitated product to exchange with Cl^- ions, resulting in large lattice mismatch, strain release, and formation of void-like mesopores. The prepared BiOCl MSCN photocatalyst exhibits excellent catalytic performance with 99% conversion and 98% selectivity for oxidation of benzyl alcohol to benzaldehyde and superior general adaptability for various aromatic alcohols. The theoretical calculations and characterizations confirm that the superior performance is mainly attributed to the abundant oxygen vacancies, plenty of accessible adsorption/active sites and fast charge transport path without grain boundaries.

Facet synergy dominant Z-scheme transition in BiOCl with enhanced 1O2 generation

BiOCl powders with different morphology were obtained through self-assembling. Their photocatalytic performance was tested through degradation of organic dye and mechanism of photocatalytic for obtained samples were investigated. Relevant characterization demonstrated that facet synergy was a main reason of photocatalytic performance promotion due to changed facet exposure and proportion under self-assembling. Theory and experimental analysis manifested that synergistic facet stimulated Z scheme transition in samples with lower (001) facet proportion, which provided favorable condition of ¹O₂ generation and simultaneously generated prominent charge separation. This work unveiled the facet synergy dominant photocatalytic performance improvement in self-assembling system of BiOCl and verified decisive role of facet proportion in constructing Z-scheme facet junction, which also prompted possibility of improving ¹O₂ generation through facet engineering under self-assembling.

Advances in facet-dependent photocatalytic properties of BiOCl catalyst for environmental remediation

Bismuth chloride oxide (BiOCl) is a typical V-VI-VII ternary oxide material, which is one of the widely studied metal oxides due to its unique surface, electronic and photocatalytic properties. However, the broad bandgap and the large number of photogenerated electron-hole pair complexes of BiOCl limit its photocatalytic efficiency. Since the photocatalytic performance of BiOCl is highly dependent on its exposed crystallographic facets, research attention has increasingly focused on the different structures and properties possessed by different crystallographic facets of BiOCl. This article reviews the basic principles of using different crystalline surfaces of BiOCl materials to enhance photocatalytic activity, summarizes the applications of BiOCl single-crystal catalysts and composite catalysts in the environmental field, and provides an outlook on the challenges and new research directions for future development in this emerging frontier area. It is hoped that the crystalline surface-related photocatalysis of BiOCl can be used to provide new guidance for the rational design of novel catalysts for various energy and environment-related applications.

Immobilization of bismuth oxychloride on cellulose nanocrystal for sunlight-driven superior photosensitized degradation

Semiconductor photocatalysis is considered to be an important green technology for sewage treatment. However, most of the pollutant degradation studies used simulated sunlight in a laboratory, which has great energy cost with limited applications in industry. Herein, cellulose nanocrystal (CNC) with rich hydroxyl groups and high specific surface area are used as the matrix to construct composites with BiOCl, which improves the dispersibility with an increased number of oxygen vacancies on BiOCl. The obtained composite photocatalyst, i.e., BiOCl/CNC, showed an excellent performance with good recyclability. Within 30 min, 99% of RhB (20 mg/L) was degraded under simulated visible light and 94% under natural sunlight. The reaction system maintains excellent catalytic performance after being scaled up by 10×. Compared with reported BiOCl-based composites in literature, BiOCl/CNC had excellent photocatalytic activity for the RhB degradation with good recyclability. Subsequently, by identifying the active species, a reasonable photocatalytic mechanism was proposed for RhB degradation. This work developed an economical and effective visible light sensitive photocatalyst for the treatment of organic dyes in water.

Mechanistic insight of structural and optical properties of BiOCl in the presence of CNTs and investigating photodegradation of phenol by BiOCl/CNT composites

In this work, we have synthesized composites of BiOCl with carbon nanotubes (CNTs) via a hydrothermal method. Different compositions of CNTs were used to study their influence on the physicochemical properties of BiOCl. Based on the interesting results obtained, various significant correlations were made. This study explored how use of CNTs and different hydrothermal crystallization conditions can influence the photocatalytic activity of composites. The CNTs have an impact on the primary crystallite size and morphology of BiOCl. Also, a higher degree of crystallization was obtained in the case of samples containing CNTs. However, in some cases, the synthesis parameters such as high temperature and longer duration also promoted crystallinity in BiOCl/CNT samples. Further, the samples were investigated for their photocatalytic activity to study the photodegradation of RhB and phenol, as model pollutants, under visible and UV light, respectively. The maximum degradation efficiency of 83% for RhB under visible light and almost 40% for phenol under UV light was obtained using BiOCl/CNT composites. Surprisingly, pure BiOCl showed higher performance for the removal of both the pollutants. This is why some comparisons and correlations between the structural and optical properties of BiOCl and CNTs were made. Finally, this study illustrates how a nanostructure like conductive multiwalled carbon nanotubes can sometimes have detrimental effects on the overall photocatalytic properties of a photocatalyst like BiOCl under certain conditions. Therefore, understanding the synergy between physico-chemical properties of BiOCl and nanostructured-modifiers like CNTs could help in designing a photocatalyst system which could benefit wastewater treatment.

In this work, we have synthesized composites of BiOCl with carbon nanotubes (CNTs) via a hydrothermal method.