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• 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]

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]