Quaternary heterostructured Ag–Bi2O2CO3/Bi3.64Mo0.36O6.55/Bi2MoO6 composite: Synthesis and enhanced visible-light-driven photocatalytic activity

Pd Nanoparticle-Decorated Novel Ternary Bi2O2CO3-Bi2MoO6-CuO Heterojunction for Enhanced Photo-electrocatalytic Ethanol Oxidation

Recently, photo-electrooxidation of fuel using a noble metal-semiconductor junction has been one of the most promising approaches in fuel cell systems. Herein, we report the development of a Pd-supported Bi2MoO6-Bi2O2CO3-CuO novel ternary heterojunction for ethanol oxidation in alkali in the presence and absence of visible light. Various spectroscopic and microscopic characterization techniques confirm strong coupling between palladium nanoparticles and Bi2MoO6-Bi2O2CO3-CuO ternary heterojunction supports. The photo-electrocatalytic efficacy of the synthesized catalysts was inspected by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). The CV study reveals that the forward peak current density (in mA mg-1 of Pd) of the synthesized quaternary heterojunction was about 1482.5, which is 2.4, 4, and 4.6 times higher than that of Pd/CuO (608.3), Pd/Bi2MoO6-Bi2O2CO3 (368.3), and similarly synthesized Pd catalyst (321.5) under visible light radiation. The best heterojunction catalyst shows 2.21-fold higher peak current density in visible light compared to that in dark. CA study reveals that after operation for 6000 s, the current density of the quaternary electrode is 1.5 and 3.4 times greater than that of Pd/CuO and Pd/C catalysts, respectively. The greater photocurrent response, lower photoluminescence (PL) emission intensity, and smaller semicircle arc in the Nyquist plot of the quaternary catalyst demonstrate the efficient segregation and higher charge transfer conductance of photogenerated charges to facilitate the photo-electrooxidation process of ethanol. The stability test shows that the quaternary catalyst loses only 9.8 and 7.7% of its maximum current density after 500 cycles of CV operation in the dark and light, respectively, indicating that light energy is more beneficial in establishing high stability. The dramatic enhancement of the photo-electrocatalytic activity of the quaternary electrode is owing to the lower band gap, high ECSA, enhanced charge separation of photogenerated carriers (e--h+), and all cocatalytic support of Bi2MoO6, Bi2O2CO3, and CuO in Pd/ Bi2MoO6-Bi2O2CO3-CuO under visible light radiation. The morphology and structure of the used quaternary catalyst are tested using FESEM and PXRD. Finally, ex situ FTIR spectroscopy and HPLC techniques help understand the ethanol electrooxidation reaction mechanism.

Photocatalytic Z-Scheme Overall Water Splitting: Recent Advances in Theory and Experiments

Photocatalytic water splitting is considered one of the most important and appealing approaches for the production of green H₂ to address the global energy demand. The utmost possible form of artificial photosynthesis is a two-step photoexcitation known as "Z-scheme", which mimics the natural photosystem. This process solely relies on the effective coupling and suitable band positions of semiconductors (SCs) and redox mediators for the purpose to catalyze the surface chemical reactions and significantly deter the backward reaction. In recent years, the Z-scheme strategies and their key role have been studied progressively through experimental approaches. In addition, theoretical studies based on density functional theory have provided detailed insight into the mechanistic aspects of some breathtakingly complex problems associated with hydrogen evolution reaction and oxygen evolution reaction. In this context, this critical review gives an overview of the fundamentals of Z-scheme photocatalysis, including both theoretical and experimental advancements in the field of photocatalytic water splitting, and suggests future perspectives.

Morphology modulation and performance optimization of nanopetal-based Ag-modified Bi2O2CO3 as an inactivating photocatalytic material

The use of photocatalytic technology to kill bacteria on marine vessel surface coatings has been paid more attention by research scholars. In this paper, petal-like microspheres with Ag nanoparticles were prepared by a simple one-step process combining the hydrothermal method and photodeposition. The 0.7% Ag/Bi₂O₂CO₃ composite photocatalyst exhibited the highest photocatalytic efficiency for bacterial removal under visible light irradiation and had the highest photogenerated carrier separation efficiency, and the sterilization rate was doubled compared with that of pure Bi₂O₂CO₃, reaching 95%. Using X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy, the existence of Ag nanoparticles was confirmed, and their size was approximately 10 nm. The surface plasmon resonance (SPR) effect of Ag nanoparticles was investigated by ultraviolet-visible diffuse reflectance spectroscopy (DRS). It was shown that the surface plasmon resonance effect of Ag improved the spectral utilization of the Ag/Bi₂O₂CO₃ composite photocatalyst and enhanced the stability of the catalyst. This caused the Ag/Bi₂O₂CO₃ composite photocatalyst to have superior photocatalytic activity to pure Bi₂O₂CO₃. The results of electrochemical impedance characterization and transient photocurrent response show that 0.7% Ag/Bi₂O₂CO₃ has a high efficiency of photogenerated carrier separation. By the free radical capture test, hydroxyl radicals were the primary active substance, and Ag⁺ improved the photocatalytic sterilization activity.

Photocatalysis for Organic Wastewater Treatment: From the Basis to Current Challenges for Society

Organic pollutants such as dyes, antibiotics, analgesics, herbicides, pesticides, and stimulants become major sources of water pollution. Several treatments such as absorptions, coagulation, filtration, and oxidations were introduced and experimentally carried out to overcome these problems. Nowadays, an advanced technique by photocatalytic degradation attracts the attention of most researchers due to its interesting and promising mechanism that allows spontaneous and non-spontaneous reactions as they utilized light energy to initiate the reaction. However, only a few numbers of photocatalysts reported were able to completely degrade organic pollutants. In the past decade, the number of preparation techniques of photocatalyst such as doping, morphology manipulation, metal loading, and coupling heterojunction were studied and tested. Thus, in this paper, we reviewed details on the fundamentals, common photocatalyst preparation for coupling heterojunction, morphological effect, and photocatalyst’s characterization techniques. The important variables such as catalyst dosage, pH, and initial concentration of sample pollution, irradiation time by light, temperature system, durability, and stability of the catalyst that potentially affect the efficiency of the process were also discussed. Overall, this paper offers an in-depth perspective of photocatalytic degradation of sample pollutions and its future direction.

Facile Formation of Bi2O2CO3/Bi2MoO6 Nanosheets for Visible Light-Driven Photocatalysis

Bi2O2CO3/Bi2MoO6 heterojunction catalysts were prepared by treating Bi2MoO6 sheets with aqueous NaHCO3 solutions at room temperature. All the Bi2O2CO3/Bi2MoO6 heterojunctions exhibited higher activities than pristine Bi2MoO6 in the photocatalytic degradation of rhodamine B (RhB), methyl orange, and ciprofloxacin under visible-light irradiation, and the most active photocatalyst was found to be the one with a C/Bi molar ratio of ∼1/2.3. Relevant samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, Fourier transform infrared spectroscopy, and UV-vis spectroscopy. The higher activity of Bi2O2CO3/Bi2MoO6 than pristine Bi2MoO6 is explained by the enhanced separation and transfer of photogenerated electron/hole pairs, as verified by transient photocurrent densities, photoluminescence spectroscopy, and electrochemical impedance spectroscopy. Photogenerated holes (h+) and superoxide radical anions (•O2 -) were found to be the main active species. The good reusability of Bi2O2CO3/Bi2MoO6 was testified by cycling degradation of RhB and tetracycline hydrochloride.

BiOBr/Bi2MoO6 composite in flower-like microspheres with enhanced photocatalytic activity under visible-light irradiation

BiOBr/Bi₂MoO₆ flower-like microspheres synthesized by a facile solvothermal method, exhibited high photocatalytic activity owing to the enhanced light harvesting via multiple-reflections and the reduced photoelectron–hole recombination.