Synthesis of Reduced Graphene Oxide Supported Flower-like Bismuth Subcarbonates Microsphere (Bi 2 O 2 CO 3 -RGO) for Supercapacitor Application

Battery-like bismuth oxide anodes for soft-packed supercapacitors with high energy storage performance

Bismuth compounds are of interest because of abundant reserves and high theoretical capacity for use as anodes in supercapacitors. In this work, bismuth oxycarbonate is synthesized by a hydrothermal method, and bismuth oxide is obtained by the subsequent calcination process, both of which possess high specific capacity. In particular, Bi₂O₃ possesses a specific capacity of 1178 F g^-1 (1178 C g^-1, 327 mA h g^-1) at a current density of 1 A g^-1, and still retains 94.9% capacity at 20 A g^-1, indicating excellent rate capability. Furthermore, Ni(OH)₂ is prepared with a specific capacity of 2447 F g^-1 at 1 A g^-1. Using Bi₂O₃ as the anode and Ni(OH)₂ as the cathode, respectively, the soft-packed supercapacitors are assembled with a large voltage window of 1.75 V. The energy density is as high as 139.7 W h kg^-1 at a power density of 874.8 W kg^-1. Even at 18 000 W kg^-1, the device retains an energy density of 94 W h kg^-1. Connecting two devices in series as a power source can light up 88 light emitting diodes (LEDs) for 2 hours, and drive a tiny fan to run for 18 seconds. The work provides new ways for the practical application of supercapacitors.

Er3+/Sm3+ co-doped Bi2O2CO3 in photocatalytic water treatment: Immobilization, acute toxicity, sterilization, and catalytic oxidation activity

Defect construction and rare earth doping are the linchpins to completing the target of partial electronic regulation. In Er³⁺/Sm³⁺ co-doping Bi₂O₂CO₃, rare earth doping resulted in the exposure of {001} crystal plane in Bi₂O₂CO₃ and cause surface defects and electron traps, achieving wide light response capability and fast carrier separation. Furthermore, a potential TC degradation route was acknowledged derived from LC-MS. Then, the median lethal concentration LC50 (96 h) is 80 ppm, probing the 2E2SBOC photocatalyst has low toxicity in actual wastewater. Combining with immobilization technology, not only does it have little impact on the organisms in the wastewater, but it is easy to recycle after degradation. In terms of new water disinfection technology, bacterial experiments in natural waters proved that 2E2SBOC has a potential disinfection system, which promotes the exposure of more active sites during degradation. This effective project offers a novel perspective for the development and application of rare-earth-doped photocatalysts.

Construction of Z-scheme Ag-AgBr/Bi2O2CO3/CNT heterojunctions with remarkable photocatalytic performance using carbon nanotubes as efficient electronic mediators

It is a useful strategy to use a solid electronic mediator with good conductivity to assist the separation of semiconductor photo-induced electron-hole pairs and the redox of semiconductor materials. In order to construct a photocatalyst for more efficient photocatalytic degradation of antibiotics, a simple hydrothermal and precipitation method was used to construct the Ag-AgBr/Bi₂O₂CO₃/CNT Z-scheme heterojunction by using carbon nanotubes (CNTs) as electronic mediators. Compared with the pristine AgBr, Bi₂O₂CO₃, Bi₂O₂CO₃/CNT, the 30%Ag-AgBr/Bi₂O₂CO₃/CNT photocatalyst has better photocatalytic activity under visible light irradiation, showing the best degradation ability to tetracycline (TC). Meanwhile, the photocatalytic properties of 30%Ag-AgBr/Bi₂O₂CO₃/CNT in different pH and inorganic ions were studied. Finally, the degradation pathway and catalytic mechanism of 30%Ag-AgBr/Bi₂O₂CO₃/CNT photocatalytic degradation of TC were also argued. The construction of the Z-scheme electron transport pathway, in which CNTs were used as electronic mediators, and the SPR effect of Ag and Bi metal, which enable the effective separation and transfer of photo-generated electron-hole pairs, are responsible for the significant improvement in photocatalytic performance. It opens up new possibilities for designing and developing high-efficiency photocatalysts with CNTs as the electronic mediator.

Template-free synthesis of Bi2O2CO3 hierarchical nanotubes self-assembled from ordered nanoplates for promising photocatalytic applications

In this study, we have adopted a one-step hydrothermal route to synthesize an interesting type of Bi₂O₂CO₃ hierarchical nanotubes self-assembled from ordered nanosheets. The effects of reaction time on the morphological and structural evolution, light absorption properties, photoelectrochemical performance, and photocatalytic performance of the prepared hierarchical nanotubes were investigated. Among the products synthesized at different reaction times, the 3-hour-derived Bi₂O₂CO₃ hierarchical nanotubes were identified to possess the highest photocatalytic performance. To promote the photocatalytic application of the as-synthesized Bi₂O₂CO₃ hierarchical nanotubes, their performance was systematically evaluated via the photodegradation of various organic pollutants (e.g., methyl orange (MO), rhodamine B (RhB), methylene blue (MB), ciprofloxacin (CIP), sulfamethoxazole (SMX) and tetracycline hydrochloride (TC)) and the photoreduction of Cr(VI) under simulated-sunlight irradiation. Furthermore, their photocatalytic performance was also evaluated by purifying simulated industrial wastewater (i.e., a MO/RhB/MB mixed solution) at different pH values and containing different inorganic anions. Based on the experimental data and density functional theory (DFT) calculations, the involved photocatalytic mechanism was discussed.

Fabrication of magnetic Fe3O4@SiO2@Bi2O2CO3/rGO composite for enhancing its photocatalytic performance for organic dyes and recyclability

A novel magnetic Fe₃O₄@SiO₂@Bi₂O₂CO₃/rGO composite comprising of uniform core-shell-structured Fe₃O₄@SiO₂@Bi₂O₂CO₃ microspheres mounted on reduced graphene oxide (rGO) sheets was successfully fabricated by using a facile hydrothermal method. The adsorption-desorption isotherm of Fe₃O₄@SiO₂@Bi₂O₂CO₃/rGO belonged to type IV with an H4-type hysteresis loop. The specific surface areas and magnetization saturation value (M_s) of Fe₃O₄@SiO₂@Bi₂O₂CO₃/rGO (x = 0.15 g) were 102.12 m²/g and 25.4 emu/g, respectively. Fe₃O₄@SiO₂@Bi₂O₂CO₃/rGO (x = 0.15 g) exhibited remarkable photocatalytic degradation activity and mineralization effect for MO and decolorization performance for the mixed solution of MO, Rh B, and MB. MO degradation by Fe₃O₄@SiO₂@Bi₂O₂CO₃/rGO conformed to a first-order kinetic reaction, and the corresponding k_app value was 0.05553 min^-1. A suitable amount of rGO in Fe₃O₄@SiO₂@Bi₂O₂CO₃/rGO could decrease the energy band gap, inhibit the recombination of photo-induced electron/hole (e^-/h⁺) pair, and broaden and enhance the response of the catalyst to visible light, thereby enhancing the visible-light catalytic degradation of organic dyes. The active species produced in the photocatalysis included •O₂^-, •OH, and h⁺, with •O₂^- being the dominant active species. The as-prepared photocatalyst also showed excellent magnetic separation performance and stability. Results show that the as-prepared Fe₃O₄@SiO₂@Bi₂O₂CO₃/rGO composite is a promising photocatalyst with considerable application potential in organic dyes removal.

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.