Insight into the mechanisms of combined toxicity of cadmium and flotation agents in luminescent bacteria: Role of micro/nano particles.

Currently, risk assessment and pollution management in mines primarily focus on toxic metals, with the flotation agents being overlooked. However, the combined effects of metals and flotation agents in mines remain largely unknown. Therefore, this study aimed to evaluate the combined effects of Cd and two organic flotation agents (ethyl xanthate (EX) and diethyldithiocarbamate (DDTC)), and the associated mechanisms. The results showed that Cd + EX and Cd + DDTC exhibited synergistic toxicity. The EC50 values for luminescent bacteria were 1.6 mg/L and 1.0 mg/L at toxicity unit ratios of 0.3 and 1, respectively. The synergistic effects were closely related with the formation of Cd(EX)2 and Cd(DDTC)2 micro/nano particles, with nano-particles exhibiting higher toxicity. We observed severe cell membrane damage and cell shrinkage of the luminescent bacteria, which were probably caused by secondary harm to cells through the released CS2 during their decomposition inside cells. In addition, these particles induced toxicity by altering cellular levels of biochemical markers and the transcriptional levels of transport proteins and lipoproteins, leading to cell membrane impairment and DNA damage. This study has demonstrated that particulates formed by Cd and flotation agents contribute to the majority of the toxicity of the binary mixture. This study helps to better understand the complex ecological risk of inorganic metals and organic flotation agents in realistic mining environments.

Promoting Piezocatalytic H2 O2 Production in Pure Water by Loading Metal-Organic Cage-Modified Gold Nanoparticles on Graphitic Carbon Nitride.

Piezocatalytic hydrogen peroxide (H2 O2 ) production is a green synthesis method, but the rapid complexation of charge carriers in piezocatalysts and the difficulty of adsorbing substrates limit its performance. Here, metal-organic cage-coated gold nanoparticles are anchored on graphitic carbon nitride (MOC-AuNP/g-C3 N4 ) via hydrogen bond to serve as the multifunctional sites for efficient H2 O2 production. Experiments and theoretical calculations prove that MOC-AuNP/g-C3 N4 simultaneously optimize three key parts of piezocatalytic H2 O2 production: i) the MOC component enhances substrate (O2 ) and product (H2 O2 ) adsorption via host-guest interaction and hinders the rapid decomposition of H2 O2 on MOC-AuNP/g-C3 N4 , ii) the AuNP component affords a strong interfacial electric field that significantly promotes the migration of electrons from g-C3 N4 for O2 reduction reaction (ORR), iii) holes are used for H2 O oxidation reaction (WOR) to produce O2 and H+ to further promote ORR. Thus, MOC-AuNP/g-C3 N4 can be used as an efficient piezocatalyst to generate H2 O2 at rates up to 120.21 µmol g-1 h-1 in air and pure water without using sacrificial agents. This work proposes a new strategy for efficient piezocatalytic H2 O2 synthesis by constructing multiple active sites in semiconductor catalysts via hydrogen bonding, by enhancing substrate adsorption, rapid separation of electron-hole pairs and preventing rapid decomposition of H2 O2 .

Water flow promoted charge separation in piezoelectric Bi4Ti3O12 for the enhanced photocatalytic degradation of antibiotic.

Addressing the issue of antibiotic residues in the environment is key to improving the quality of aquatic environments and reducing human health risks. In this study, piezoelectric bismuth titanate (Bi4Ti3O12) nanosheets are synthesized and employed to conduct antibiotic degradation. The piezoelectric potential induced by the water flow shear force is utilized to facilitate charge separation and migration in the photocatalytic process and enhance the catalytic degradation of antibiotic wastewater. As a result, 85% of tetracycline hydrochloride (TC) is degraded within 90 min. The piezo-photocatalytic process exhibits a 2.4 times faster reaction rate and a 15% higher mineralization rate than photocatalysis. Different environmental factors are investigated for their effects on the catalytic activity in piezo-photocatalysis. In situ electrochemical measurement and photoluminescence (PL) spectroscopy under stress demonstrated that the piezoelectric potential shifted the energy band of Bi4Ti3O12 and promoted the charge migration and separation, which produce more active species that favor the efficient catalytic degradation. Finally, the intermediate products of the tetracycline hydrochloride degradation process are analyzed and possible degradation pathways are suggested. This study elucidates the degradation mechanism of Bi4Ti3O12 as a piezo-photocatalyst for antibiotic pollutants, and meticulously investigates the charge transfer mechanism of the catalyst material in response to micro-stress. Hence, it provides an efficient solution for organic wastewater treatment and can potentially provide theoretical support for the development and performance optimization of catalyst materials applied in natural environments.

Efficient piezo-photocatalysis of 0D/2D α-Fe2O3/Bi2WO6: Synergy of weak force-driven piezoelectric polarization and Z-scheme junction.

Photocatalysis shows huge potential in environmental purification, but suffers from fast photocharge recombination and finite photoabsorption. Piezoelectric polarization is perceived as a promising approach to drive charge separation, but it always relies on the energy-guzzling ultrasonic vibration. Herein, a piezo-photocatalytic system integrating dual electric fields constructed by weak force-driven piezoelectric polarization and Z-scheme junction is developed in 0D/2D α-Fe2O3/Bi2WO6. The introduction of low-frequency water flow-induced piezoelectric polarization field accelerates the migration of bulk photoexcited carriers of polar Bi2WO6, and forming Z-scheme junction with intimate interface guarantees the spatial separation of interfacial charges and strong visible light response. Benefiting from these merits, water flow-triggered α-Fe2O3/Bi2WO6 delivers a superb tetracycline hydrochloride photodegradation efficiency of 82% within 20 min, which outperforms related piezo-photocatalysts in previous reports, even those driven by high-frequency ultrasound. KPFM and DFT calculations provide forceful evidence for the Z-scheme transfer pathway between α-Fe2O3 and Bi2WO6. Additionally, the synergetic effect of constructing the Z-scheme junction and introducing piezoelectric polarization is well confirmed by PFM, COMSOL simulation, ESR and photoelectrochemical characterization. This work offers a novel strategy to design the piezo-photocatalytic system and maybe realize the in-situ treatment of sewage taking full advantage of hydrodynamic characteristics.

Mineral phase transition characteristics and its effects on the stabilization of heavy metals in industrial hazardous wastes incineration (IHWI) fly ash via microwave-assisted hydrothermal treatment.

Toxic heavy metals in industrial hazardous waste incineration (IHWI) fly ash can be effectively stabilized by using microwave-assisted hydrothermal technology. However, few works have focused on the relationship between mineralogical conversion and stability of heavy metals of fly ash during hydrothermal process. This study investigated the effect of mineral phase transition process on the stabilization and migration behavior of heavy metals in IHWI fly ash using coal fly ash as silicon­aluminum additive. Mineral composition analysis reveals that after microwave-assisted hydrothermal treatment (MAHT) of IHWI fly ash, zeolite-like minerals (e.g., tobermorite, katoite and sodalite), secondary aluminosilicate minerals (e.g., prehnite and anorthite) and other newly-formed minerals (e.g., wollastonite, pectolite and larnite) were found. The leaching concentrations of heavy metals (Cr, Ni, Cu, Zn, Cd and Pb) in IHWI fly ash decrease sharply after MAHT with the most obvious decreases in Cu, Pb and Zn. Spearman correlation analysis show significantly negative correlation between the content of zeolite-like minerals and the leaching concentrations of most heavy metals (e.g., Ni, Cu, Zn, Cd and Pb). These results suggest that the immobilization effects of heavy metals in IHWI fly ash can be effectively enhanced by promoting the formation of zeolite-like minerals during the MAHT. This study is expected to further promote the development of IHWI fly ash harmless treatment technology.

Photocatalysis Enhanced by External Fields.

The efficient conversion of solar energy by means of photocatalysis shows huge potential to relieve the ongoing energy crisis and increasing environmental pollution. However, unsatisfactory conversion efficiency still hinders its practical application. The introduction of external fields can remarkably enhance the photocatalytic performance of semiconductors from the inside out. This review focuses on recent advances in the application of diverse external fields, including microwaves, mechanical stress, temperature gradient, electric field, magnetic field, and coupled fields, to boost photocatalytic reactions, for applications in, for example, contaminant degradation, water splitting, CO2 reduction, and bacterial inactivation. The relevant reinforcement mechanisms of photoabsorption, the transport and separation of photoinduced charges, and adsorption of reagents by the external fields are highlighted. Finally, the challenges and outlook for the development of external-field-enhanced photocatalysis are presented.

Ferroelectric spontaneous polarization steering charge carriers migration for promoting photocatalysis and molecular oxygen activation.

Introducing a polarization electric field in photocatalyst system is regarded asa new concept for photocatalytic activity enhancement. In this work, we first unearth that the spontaneous polarization of ferroelectric BaTiO3 promotes the photocatalytic and molecular oxygen activation performance of the narrow-band-gap semiconductor BiOI. Ferroelectric tetragonal-phase BaTiO3 (T-BaTiO3) were prepared via calcination of nonferroelectric cubic-phase BaTiO3 (C-BaTiO3), and their polarization ability was verified via ultrasonication-assisted piezoelectric catalytic degradation. Then, the C-BaTiO3/BiOI and T-BaTiO3/BiOI heterostructures are fabricated by a soft-chemical method. To disclose the influence of ferroelectric spontaneous polarization on charge movement behavior, the photocatalytic and molecular oxygen activation properties are monitored by degradation of methyl orange (MO) and superoxide radical (O2-) evolution under visible light irradiation (λ>420nm), respectively. The results demonstrated that T-BaTiO3/BiOI far outperforms C-BaTiO3/BiOI and pristine BiOI. The ferroelectric spontaneous polarization of T-BaTiO3 can steer the migration of photogenerated charge carriers and induce efficient separation, accounting for the strengthened photodegradation and reactive oxygen species O2- production rate (11.02×10-7molL-1h-1). The study may furnish a new reference for developing efficient tactics to advance the photocatalytic and molecular oxygen activation ability for environmental chemistry and biochemistry applications.

Macroscopic Polarization Enhancement Promoting Photo- and Piezoelectric-Induced Charge Separation and Molecular Oxygen Activation.

Efficient photo- and piezoelectric-induced molecular oxygen activation are both achieved by macroscopic polarization enhancement on a noncentrosymmetric piezoelectric semiconductor BiOIO3 . The replacement of V5+ ions for I5+ in IO3 polyhedra gives rise to strengthened macroscopic polarization of BiOIO3 , which facilitates the charge separation in the photocatalytic and piezoelectric catalytic process, and renders largely promoted photo- and piezoelectric induced reactive oxygen species (ROS) evolution, such as superoxide radicals (. O2- ) and hydroxyl radicals (. OH). This work advances piezoelectricity as a new route to efficient ROS generation, and also discloses macroscopic polarization engineering on improvement of multi-responsive catalysis.