Fabrication of Hydrotalcite-like Copper Hydroxyl Salts as a Photocatalyst and Adsorbent for Hexavalent Chromium Removal

Chitiphon Chuaicham,Li Zhang,Vellaichamy Balakumar,Karthikeyan Sekar,Siwaporn Meejoo Smith,Jirawat Trakulmututa,Keiko Sasaki

doi:10.3390/min12020182

Chitiphon Chuaicham, Li Zhang + Show 5 more

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https://doi.org/10.3390/min12020182

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Journal: Minerals	Publication Date: Jan 30, 2022
Citations: 5	License type: CC BY 4.0

Affiliation: Kyushu University, Mahidol University

Abstract

Cu-HyS-urea and Cu-HyS-NaOH, which are hydrotalcite-like copper hydroxyl salts, were prepared by two different methods, urea hydrolysis and precipitation, respectively. Both synthesis methods provided the successful formation of a copper hydroxyl salt, Cu2(OH)3NO3. From XRD and UV-DRS results, the product from the urea hydrolysis methods (Cu-HyS-urea) displayed higher crystallinity, small bandgap energy (Eg), and high light absorption ability because of some intercalated carbonate anions. For the Cr(VI) removal test, the Cu-HyS-NaOH showed superior adsorption of Cr(VI) than Cu-HyS-urea due to a higher specific surface area, confirmed by BET analysis. However, the Cu-HyS-urea presented higher photocatalytic Cr(VI) reduction under light irradiation than Cu-HyS-NaOH, owing to narrow Eg, less recombination, and a high transfer of the photogenerated charge carriers, proven by the results from photoluminescence, photocurrent density, and electrochemical impedance spectroscopy. Thus, this work provides a new function of the hydrotalcite-like copper hydroxyl salts (Cu-HyS-urea and Cu-HyS-NaOH) that can be utilized not only for adsorption of Cr(VI) but also as photocatalysts for Cr(VI) reduction under light irradiation.

Highlights

The hydrotalcite-like hydroxy salt (HyS) materials have been reported in one type of layered metal hydroxides, with the general formula M2+(OH)2−x(Am−)x/m·nH2O, where M2+ is the divalent metal cation (Mg2+, Ni2+, Zn2+, Ca2+, Cd2+, Co2+, and Cu2+) and Am− is the counterion, such as nitrate and carbonate anions, which are exchangeable anions [1]
The results from PL spectroscopy, transient photocurrent density, and electrochemical impedance spectroscopy (EIS) measurements confirmed the hydrotalcite-like copper hydroxyl salts from urea hydrolysis (Cu-HyS-urea) can provide a higher charge separation and production due to small Eg and high crystallinity
Hydrotalcite-like copper hydroxyl salts (Cu-HyS-urea and Cu-HyS-NaOH) were successfully synthesized by two different methods, which were urea hydrolysis and precipitation, and they were applied for the removal of 10 ppm Cr, which is a toxic inorganic pollutant in wastewater

Summary

Introduction

The hydrotalcite-like hydroxy salt (HyS) materials have been reported in one type of layered metal hydroxides, with the general formula M2+(OH)2−x(Am−)x/m·nH2O, where M2+ is the divalent metal cation (Mg2+, Ni2+, Zn2+, Ca2+, Cd2+, Co2+, and Cu2+) and Am− is the counterion, such as nitrate and carbonate anions, which are exchangeable anions [1]. Copper hydroxy salt (Cu2(OH)3NO3, Cu-HyS) has been focused to be an environmentally friendly material to remove toxic pollutants in wastewater [2,3,4,5,6,7,8,9]. Cu octahedral layers are stacked upon each other to form the lamellar structure, containing two forms of copper octahedral: Cu(1) is coordinated by four OH− groups and two oxygen atoms belonging to NO3− groups. For another Cu(2) species, four hydroxyls coordinate the Cu(2) atoms, with the fifth OH standing a little further away and an oxygen atom belonging to the NO3−

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