Microspheres of graphene oxide coupled to N-doped Bi2O2CO3 for visible light photocatalysis

Constructing 3D flower-like S-scheme N-Bi2O2CO3/g-C3N4 heterojunction with enhanced photocatalytic performance

Mineral processing wastewater contains a lot of organic matter and heavy metal ions, and poor self-degradation ability makes it a key treatment object in environmental treatment. Photocatalysis is a promising technology to efficiently mineralize refractory contaminants from wastewater. In this work, 3D flower-like S-scheme N-Bi2O2CO3/g-C3N4 heterostructures were successfully constructed by hydrothermal method with the auxiliary of ionic liquids. The photocatalytic experiments show that the catalytic activity of heterojunction photocatalysts was significantly higher than that of bare g-C3N4 and N-Bi2O2CO3 for the degradation of two pollutants. NBOC/CN-2 shows the highest photocatalytic performance, and the degradation efficiency of sodium isobutyl xanthate (SIBX) on NBOC/CN-2 is 1.85 and 3 times that of bare g-C3N4 and Bi2O2CO3, respectively. The degradation efficiency of m-Cresol on NBOC/CN-2 is 8.34 and 6.93 times that of bare g-C3N4 and N-Bi2O2CO3, respectively. This significantly enhanced photocatalytic activity is attributed to the formation of flower-like heterojunctions, which can greatly increase the specific surface area and facilitate the separation and migration of photogenerated carriers. Total organic carbon (TOC) experiment proves that the two pollutants are effectively mineralized under the action of the prepared photocatalyst. The degradation path of m-Cresol degradation products was inferred based on the ion fragments. The capture experiment and Nitro-blue tetrazolium (NBT)-•O2- measurement show that superoxide radical plays a major role in photocatalytic degradation. The outstanding stability of the prepared flower-like heterojunction samples was examined by cyclic experiments. The S-scheme charge transfer mechanism has been proposed to explain the boosted activity of the flower-like heterojunction photocatalyst. This work provides a new idea for the design of efficient and stable g-C3N4-based photocatalyst for the photocatalytic degradation of refractory wastewater.

Typical layered structure bismuth-based photocatalysts for photocatalytic nitrogen oxides oxidation

Traditional NO_x treatment methods require external reducing reagents and harsh reaction conditions, which is not conducive to effectively eliminate NO_x at low concentration, especially at ppb levels. Fortunately, low concentration NO_x can be removed by photocatalytic oxidation under mild reaction conditions. Bismuth (Bi)-based photocatalysts with the layered structure have obtained considerable concerns of photocatalytic NO_x oxidation. This review focused on typical layered Bi-based photocatalysts (Bi₂WO₆, Bi₂O₂CO₃, BiOY (YCl, Br, and I), BiOIO₃, and BiOCOOH) with the structure of [Bi₂O₂]²⁺ layer for photocatalytic NO_x oxidation. The strategies (morphological control, defect engineering, heterostructure construction, etc.) to improve photocatalytic oxidation activity were summarized. Furthermore, the mechanism involving various free radicals (hydroxyl radical, superoxide radical, etc.) of photocatalytic oxidation of NO_x was proposed. In addition, the non-NO₂ selectivity was also illuminated. Lastly, the current drawbacks and further research directions for photocatalytic NO_x oxidation were elaborated. The development of photocatalysts with high photocatalytic activity, wide light absorption range, and non-NO₂ selectivity is the focus of future research. This review aims to provide a pandect and theoretical guidance for the practical application of photocatalytic oxidation of NO_x.

Heterostructured Bi2O2CO3/rGO/PDA photocatalysts with superior activity for organic pollutant degradation: Structural characterization, reaction mechanism and economic assessment

Compared with conventional methods for organic pollutant degradation, photocatalysis is a promising treatment technology with broad application prospects. Bi₂O₂CO₃ is often used for organic pollutants degradation but greatly restricted by having drawbacks of large band gap and high electron-hole recombination rate. Herein, heterostructured Bi₂O₂CO₃ (BOC)/reduced graphene oxide (rGO)/polydopamine (PDA) (BGP) photocatalysts were first designed through a green chemical method. By incorporating rGO and PDA in BOC, the kinetic constant of BGP to catalytically degrade methyl orange (MO) was significantly increased; over fourfold elevated rather than that of BOC (k_app/BOC = 0.0019, k_app/BGP = 0.0089) due to the high electron transfer capability of rGO and superior adhesive force and semiconducting properties of PDA. DRS and photoelectrochemical results confirmed the improvement of the light absorption range and charge transfer capability because of the synergistic effect of rGO and PDA. Results of trapping experiment and ESR unraveled the catalytic mechanism that both holes (h⁺) and superoxide radicals (•O₂^-) were the main oxidative species for MO degradation. Economic assessment results demonstrated that Bi₂O₂CO₃/rGO/PDA heterojunctions have great potentials in the field of organic wastewater purification. This study developed a low-cost and highly efficient BGP material and provided a deep understanding of the structure-performance relationships of materials for organic pollutant degradation.