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• Clay spatially confined the growth of layered basic zinc acetate nanosheets. • Thermal-induced nano-cracking leaded to clay-supported ZnO nanoparticles. • Layered basic zinc acetate improve clay to adsorb Congo red. • Well-dispersed ZnO nanoparticles endowed clay with photocatalytic activity. Here, hierarchical nanostructures of clay-based hybrids were synthesized via a space-confined growth of layered basic zinc acetate (LBZA) nanosheets standing upright on both sides of bentonite clay platelets. These thermally instable LBZA nanosheets were thermally decomposed and fragmented into ZnO nanoparticles well-dispersed on bentonite platelets. The morphology and structure of LBZA/bentonite and ZnO/bentonite was characterized by SEM, TEM, XRD, TG-DSC, and FTIR. Surface density of LBZA nanosheets on bentonite platelets was simply controlled by tuning the amount of zinc acetate. LBZA/bentonite and ZnO/bentonite was used for the adsorption of Congo red (CR) and photodegradation of methyl orange (MO), respectively. Results showed that LBZA/bentonite exhibited higher adsorption capacity for Congo red (CR) than original bentonite. In addition, bentonite-supported ZnO nanoparticles efficiently promoted the photodegradation of MO under UV light irradiation. [ABSTRACT FROM AUTHOR]

• Non-aqueous phase synthesis of halloysite-supported Co 3 O 4 nanoparticles. • Halloysite-induced generation of Co3+-rich and small-sized Co 3 O 4 nanoparticles. • Co 3 O 4 /halloysite for enhancing catalytic reduction of 4-nitrophenol and organic dyes. • Co 3 O 4 /halloysite promoting to shorten induction time of 4-nitrophenol reduction. Nanosized clay minerals have been widely used as efficient supports to immobilize catalyst nanoparticles. However, clay support-induced interactions and their influences on the catalyst structure and performance currently have not been fully understood. Here, Co 3 O 4 nanoparticles supported on halloysite nanotubes (HNTs) were synthesized by a facile deposition-precipitation approach followed by thermal treatment. A series of characterization methods were employed for the Co 3 O 4 /HNTs hybrid nanostructure to identify its crystal phase, chemical composition, morphology, specific surface area, surface chemical states, and redox property. Characterization results showed that HNTs not only impacted the particle size of Co 3 O 4 nanoparticles, but also modified surface chemical surface states of the later, which ultimately promoted the effective catalytic reduction of 4-nitrophenol (4-NP) and azo dyes with sodium borohydride. The interaction between HNTs and Co 3 O 4 nanoparticles was found to shorten the induction period of the 4-NP reduction. Meanwhile, the Co 3 O 4 /HNTs catalyst for the 4-NP reduction achieved an apparent rate constant of 0.265 min−1 and an activity parameter of 1.63 × 104 min−1 g−1 as well as a turnover frequency of 4.37 min−1. In addition, Co 3 O 4 /HNTs showed an improvement in reduction efficiency of the azo dyes when compared to bare Co 3 O 4 nanoparticles. [ABSTRACT FROM AUTHOR]

Microbial treatment of Cr(VI) is an environmentally friendly and low-cost approach. However, the mechanism of mutualism and the role of interspecies electron transfer in Cr(VI) reducing microflora are unclear. Herein, we constructed an intersymbiotic microbial association flora to augment interspecies electron transfer via functionalizing electroactive Shewanella oneidensis MR-1 with metal-reducing microflora, and thus the efficiency of Cr(VI) reduction. The findings suggest that the metal-reducing active microflora could converts glucose into lactic acid and riboflavin for S. oneidensis MR-1 to act as a carbon source and electron mediator. Thus, when adding initial 25 mg/L Cr (VI), this microflora exhibited an outstanding Cr (VI) removal efficiency (100%) at 12 h and elevated Cr (III) immobilization efficiency (80%) at 60 h with the assistance of 25 mg/L Cu(II). A series of electrochemical experiments proved this remarkable removal efficiency were ascribed to the improved interspecies electron transfer efficiency through direct interspecies electron transfer and riboflavin through mediated interspecies electron transfer. Furthermore, the metagenomic analysis revealed the expression level of the electron transport pathway was promoted. Intriguing high abundance of genes participating in the bio-reduction and biotransformation of Cr(VI) was also observed in functional microflora. These outcomes give a novel strategy for enhancing the reduction and fixation of harmful heavy metals by coculturing function microflora with electrogenic microorganisms. [Display omitted] • An intersymbiotic microflora was constructed by functionalizing S. oneidensis MR-1 with metal-reducing bacteria. • The microflora achieved Cr(VI) removal efficiency of 100% and Cr (III) immobilization efficiency of 80%. • The removal efficiency was ascribed to the improved interspecies electron transfer. • The metal-reducing active microflora converted glucose to lactate and riboflavin for S. oneidensis MR-1 to utilize. • The metagenomic analysis revealed the expression level of the electron transport pathways were promoted. [ABSTRACT FROM AUTHOR]

Chromium ore processing residue (COPR) is a hazardous waste generated during the production of chromate. Currently, approximately 10% of Cr 2 O 3 cannot be extracted after chromite sodium roasting and remains in COPR, wasting valuable Cr resources. In this study, Mg was selectively removed by using (NH 4) 2 SO 4 roasting in combination with H 2 SO 4 leaching. The results showed that the selective removal of 79.55% Mg from COPR could be achieved under the optimum (NH 4) 2 SO 4 roasting conditions (80 mmol (NH 4) 2 SO 4 , 800 °C, 2 h). During the subsequent sodium roasting and acid leaching stages, the Cr extraction rate was 84.63% for the COPR direct roasting and 95.39% for the Mg removal residue roasting. The increased Cr extraction efficiency is attributed to the transformation of Mg-rich spinel and diopside (the Mg & Cr coexisting phases) in COPR converted into easily extractable (Fe,Cr) 2 O 3 and Cr 2 O 3 after the Mg treatment. This study investigated that the phase transformation of the Cr host phases is crucial for the sufficient extraction of Cr and provides inspiration for the development of efficient and practical Cr extraction techniques. Moreover, the method can be extended to the effective extraction of Cr from other Cr-containing wastes. [Display omitted] • The Cr host phases in COPR are Mg-containing spinel and Mg-containing diopside. • Selective pre-removal of Mg can effectively enhance the extraction of Cr from COPR. • The phase transformation of Cr-containing wastes is critical for Cr extraction. [ABSTRACT FROM AUTHOR]

Sulfidated nanoscale zero-valent iron (S-nZVI) has shown excellent removal capacity for the removal of cadmium (Cd) in aqueous phase. Herein, the effectiveness and the mechanism of S-nZVI for the remediation of Cd contaminated soil were investigated for the first time. The results of sequential extraction procedures (SEP) showed that the exchangeable (EX) Cd was decreased by over 97.6% at the optimal dosage of 5 g kg-1 S-nZVI during 30 d incubation and converted to less available Cd such as iron-manganese oxides-bound (OX) and organic matter-bound (OM) fractions. pH has negligible effect on the immobilization of Cd in soil, since OX fraction was stabilized in the range of 72–92% at initial soil pH range from 5.3 to 7.5. SEM-EDS analysis of the separated magnetic particles implied that Cd was successfully enriched on S-nZVI and the distribution of Cd was closely related to Fe, S, and O. CdO and CdS was confirmed as the key products for Cd immobilization in soil. Meanwhile, the S-nZVI was oxided to α-FeOOH, γ-FeOOH, and γ-Fe 2 O 3. The existence of CdO was visibly related to the iron oxides, suggesting the synergetic immobilization effect by iron oxides. Overall, S-nZVI was promising for the remediation of Cd-contaminated soil. [Display omitted] ● S-nZVI could effectively remediate Cd-contaminated soil. ● Exchangeable Cd fraction sharply decreased from 73% to below 1% at 3 h. ● Initial soil pH value showed a slight effect on Cd immobilization by S-nZVI. ● A potential mechanism for Cd immobilization was illustrated. [ABSTRACT FROM AUTHOR]

This work demonstrated that electroplating sludges (EPS) of specific composition may be used for the synthesis of layered double hydroxide (LDH) materials for energy applications after appropriate treatment. The unique composition and structure of EPS render it with good electrochemical energy storage performance. The EPS containing Ni, Fe, and Al was dissolved by acid and added with urea precipitator. The LDH material was prepared by a facile hydrothermal method. The increase of urea in a certain range is conducive to the formation of intact LDH. However excessive urea levels promoted the transformation from LDH to Ni(HCO 3) 2. Various active Ni bridged by N in ‒O‒C N promoted electron transfer, ‒O‒C N content in LDHs was proportional to the urea amount. The prepared LDHs exhibited a specific capacitance of 1652.20 F g−1 at 0.5 A g−1, and the value remained at 766.69 F g−1 after 1000 cycles. The prepared LDH has excellent supercapacitor performance, which is closely related to its structure. Therefore, the proposed recycling strategy of EPS resources can be used to prepare LDH supercapacitors, paving the way for new applications of EPS in the field of energy storage. ga1 • Successful synthesis of LDHs from electroplating sludge by hydrothermal method. • The as-prepared LDHs exhibited excellent supercapacitor performance. • The excellent properties of LDHs can be attributed to the formation of ‒O‒C N. [ABSTRACT FROM AUTHOR]

In this study, the reaction between sulfidated nanoscale zero-valent iron (S-nZVI) and heavy metal cations as well as the role of sulfur were investigated. The results showed the corrosion products of S-nZVI were lepidocrocite (γ -FeOOH) or/and magnetite (Fe 3 O 4), depending on heavy metal species. While the removal of Hg(II), Ag(I), Cu(II), and Pb(II) by S-nZVI was rapid and could achieve over 99% within 5 mins, the removal of Ni(II) and Zn(II) was low in efficiency and unstable. Sulfur was existed as iron sulfides at fresh S-nZVI, but was displaced by the heavy metals and formed the related sulfide compound, or oxidized to S0 and SO 4 2-. The removal mechanisms are strongly dependent on the solubility product constant (K sp) of metal sulfides. For Hg(II) and Ag(I), with K sp of corresponding metal sulfides much lower than that of iron sulfide, the removal mechanism is the displacement reaction. For Cu(II) and Pb(II), with K sp of corresponding metal sulfides moderately lower than that of iron sulfide, the removal mechanisms are the displacement reaction and complexation with surface groups of S-nZVI. For Zn(II) and Ni(II), whose K sp of corresponding metal sulfides slightly lower than that of iron sulfide, are mainly removed by complexation with surface groups of S-nZVI. ga1 The mechanism between heavy metal cations and sulfidated nanoscale zero-valent iron (S-nZVI) • S-nZVI was highly efficient for the removal of Hg(II), Ag(I), Cu(II), and Pb(II). • The role of sulfur during heavy metal cations removal by S-nZVI was investigated. • The removal mechanisms were significantly related to the metal sulfide K sp. [ABSTRACT FROM AUTHOR]