Eco‐Friendly Alkali‐Free Arginine‐Assisted Hydrothermal Synthesis of Different Layered Double Hydroxides and Their Chromate Adsorption/Reduction Efficiency

Abstract

A new one‐pot synthesis of highly crystalline MgAl‐, CoAl‐ and ZnAl‐layered double hydroxides (LDHs) containing NO3− as interlayer anion along with the surface functionalization of L‐arginine was demonstrated by the ecofriendly alkali‐free arginine‐assisted hydrothermal method to examine the adsorptive reduction of chromate (CrO42−) from aqueous solutions. The amino acid mediated water hydrolysis resulted abundant OH− in the medium, which served as precipitant, and the NO3− from metal precursor acts as an interlayer anion along with surface functionalization of amino acid. Adsorption studies revealed that the removal of CrO42− by anion exchange was the greatest in MgAl‐LDH with 1.619 mmol‐Cr/g of LDH. The mechanism of CrO42− removal was due to the ion‐exchange of NO3− from the interlayer as well as the counter anions present on the functionalized arginine cation. The adsorbed CrO42− was partially reduced to nontoxic Cr3+ on the surface of LDH due to the presence of amino acid functionalization. The present technique provides several advantages from the aspect of sustainable chemistry: (i) avoiding hazardous alkali for the preparation of LDH, (ii) removal of CrO42− by ion‐exchange and (iii) partial detoxification of CrO42− by reduction to Cr3+ on the surface of the LDH.

Synthesis of PANI/AlOOH composite for Cr(VI) adsorption and reduction from aqueous solutions

“…The high resolution of N 1s can be resolved into three different peaks at 400.7 eV, 399.4 eV and 398.1 eV (Figure C), which were assigned to the protonated amine (‐NH + ), the undoped amine‐like nitrogen atoms (‐NH‐) and the imine‐like (‐N≡) groups, respectively ,. Cr(VI) adsorption process, the proportion of ‐NH + sharply decreased from 44% to 31%, and ‐NH‐ decreased from 56% to 52% (Table ), which confirmed the redox reaction between ‐NH + and ‐NH‐ in PANI/AlOOH and Cr(VI) . The high resolution of N 1s spectra further confirmed that the amine group was in Cr(VI) removal process.…”

“…Of course, XPS analysis only provided the surface information rather than bulk concentration. Compare with PANI, more Cr(VI) was reducing to Cr(III) on PANI/AlOOH, indicating the enhanced Cr(VI) reduction ability of PANI/AlOOH . The appearance of Cr(III) species could be clearly confirmed by high resolution O 1s spectra in Figure A.…”

Synthesis and characterization of two-dimensional (2D) nanosheet zinc aluminum layered double hydroxide (Zn/Al LDH) via an alkali-free route

“…The image in Figure 2a shows a small hexagonal platelet of Zn/Al LDH material, while the image in Figure 2b shows a large hexagonal platelet. The size of hexagonal platelet of Zn/Al LDH was large as increasing in the molar ratio of Zn 2+ / Al 3+ because of more ZnO phase and ZnAl2O4 spinel were present [6]. The information about the type of bonds formed by the anions and their orientations of Zn/Al LDH material was obtained by FTIR analysis.…”

“…Research on synthesis of Zn/Al LDH via this method, where zinc nitrate solution and aluminum nitrate solution are representing as a divalent cation (M II ) and a trivalent cation (M III ) respectively, are mixed with the addition of ammonium carbonate solution under constant pH [4], [5]. The mixing of both divalent and trivalent cations can cause the electrostatic interaction between the positive and negative interlayer because of the anion exchange capacity affected by the molar ratio [6]. The studies on the different molar ratios of Zn/Al LDH can lead to changes in its structure and properties.…”

Adsorption of Hexavalent Chromium by Sodium Alginate Fiber Biochar Loaded with Lanthanum

“…The wide-scan XPS spectrum of La-BC after experiments showed that the peak of Cr element has appeared in La-BC (900℃) (Figure 8a). Moreover, the corresponding peaks where the binding capacity was 577.8 eV, 579.7 eV proved that Cr(VI) were successfully absorbed (Figure 8b) [42]. Cr has been absorbed successfully, In the La3d images, the binding energy of element La had negative displacement (0.4-0.7eV) after adsorption (Figure 8c), indicating that electron transfer occurred between La-BC (900 ℃ ) and chromite, which formed a strong chemical bond [30].…”