Two-Dimensional Cationic Aluminoborate as a New Paradigm for Highly Selective and Efficient Cr(VI) Capture from Aqueous Solution

Abstract

Water pollutants existing in their oxyanion forms have high solubility and environmental mobility. To capture these anionic pollutants, cost-effective inorganic materials with cationic frameworks and outstanding removal performance are ideal adsorbents. Herein, we report that two-dimensional (2D) cationic aluminoborate BAC(10) sets a new paradigm for highly selective and efficient capture of Cr(VI) and other oxyanions from aqueous solution. The structure of Cr(VI)-exchanged BAC(10) sample (Cr(VI)@BAC(10), H 0.22 ·Al 2 BO 4.3 ·(HCrO 4 ) 0.22 ·2.64H 2 O) has been successfully solved by continuous rotation electron diffraction. The crystallographic data show that the 2D cationic layer of BAC(10) is built by AlO 6 octahedra, BO 4 tetrahedra, and BO 3 triangles. Partial chromate ions exchanged with Cl – ions are located within the interlayer region, which are chemically bonded to the aluminoborate layer. BAC(10) shows faster adsorption kinetics compared to the commercial anion exchange resin (AER) and layered double hydroxides (LDHs), a higher maximum adsorption capacity of 139.1 mg/g than that of AER (62.77 mg/g), LDHs (81.43 mg/g), and a vast majority of cationic MOFs, and a much broader working pH range (2–10.5) than LDHs. Moreover, BAC(10) also shows excellent Cr(VI) oxyanion removal performance for a solution with a low concentration (1–10 mg/L), and the residual concentration can be reduced to below 0.05 mg/L of the WHO drinking water criterion. These superior properties indicate that BAC(10) is a promising material for remediation of Cr(VI) and other harmful oxyanions from wastewater.

Multifunctional Lanthanide Metal–Organic Frameworks Based on –NH2 Modified Ligand: Fluorescent Ratio Probe, CrO42– Ions Adsorption, and Photocatalytic Property

“…However, when the pH exceeded 6, there is a significant decrease in its adsorption of CrO 4 2– ions. The decrease in CrO 4 2– adsorption with increasing pH is attributed to additional OH – competing for adsorption on 1-Tb . The adsorption experiment of OH – ions was conducted to demonstrate this, revealing that equilibrium adsorption on 1-Tb was achieved within a span of 12 h with an adsorption capacity of 36.8 mg/g (Figure S17).…”

“…The decrease in CrO 4 2− adsorption with increasing pH is attributed to additional OH − competing for adsorption on 1-Tb. 31 The adsorption experiment of OH − ions was conducted to demonstrate this, revealing that equilibrium adsorption on 1-Tb was achieved within a span of 12 h with an adsorption capacity of 36.8 mg/g (Figure S17). It was indicated that in all cases, the optimum pH for CrO 4 2− adsorption by 1-Tb was 3, so all subsequent adsorption tests were carried out at pH = 3.…”

One-pot preparation of layered double hydroxides-engineered boric acid root and application in wastewater

“…Borates are listed as critical materials, main sources of boron, and have a wide range of industrial applications [19]. Wang et al reported the study on the effective removal of Cr(VI) by highly crystalline aluminoborate BAC (10), which was hydrothermally synthesized from a mixture of boric acid, anhydrous aluminum trichloride, and ammonium hydroxide at 150°C for 18 h [20]. However, ammonium hydroxide has the characteristics of volatility and corrosion, and it is limited in the process of use.…”