Surface Area- and Structure-Dependent Effects of LDH for Highly Efficient Dye Removal

Abstract

The surface area and structure of adsorbents are crucially important to its adsorption capacity. Herein, we focused on the correlation between the structures of 2D/3D materials and its adsorption properties by taking three kinds of cobalt−aluminum layered double hydroxide (CoAl-LDH) as adsorbents, including a 3D hierarchical flower-like hollow/solid sphere (FH/FS-CoAl) and 2D plate (P-CoAl). As expected, FH-CoAl showed the highest adsorption capacity (∼2189.23 mg/ g) for methyl orange (MO), benefiting from the highly accessible surface areas and more active sites of unique hollow structural characteristics inherited from the hierarchical flower-like hollow structures. Interestingly, compared with FS/FH-CoAl, P-CoAl exhibited the highest adsorption capacity enhancement times after being normalized with surface area, but displayed an inferior maximum adsorption capacity. The reasons could be mainly ascribed to (1) P-CoAl with 2D plate structures possessed more fully exposed active sites than FH-CoAl and (2) the compact and thick shell structure of the hollow structure made dye difficult to diffuse into the hollow interior. Moreover, the characterization analysis further confirmed that the electrostatic interaction, hydrogen bonding, and ion exchange were the main adsorption mechanisms for FH-CoAl and FS-CoAl, while electrostatic interaction was mainly an adsorption mechanism for P-CoAl. A deep understanding of synergistic modulation of surface area and structure effects of 2D/3D adsorbents will provide the opportunity for further enhancing the adsorption activity and offer a new pathway for design and optimization of advanced adsorbents in the near future.

Nature-Inspired Coral-like Layered [Co0.79Al0.21(OH)2(CO3)0.11]·mH2O for Fast Selective ppb Level Capture of Cr(VI) from Contaminated Water

“…To find out the mechanism of sorption, we carried out Fourier-transform infrared spectroscopy (FTIR) analysis, as shown in Figure c. The sharp peak at 1363 cm –1 , corresponding to CO 3 2– in CoAl-LDH, diminishes when Cr­(VI) is adsorbed on CoAl-LDH . The broad band at 3577 cm –1 , occurring because of stretching vibrations of the OH group present in the interlayered water molecules and Co/Al metal-bonded hydroxyl groups of CoAl-LDH, redshifts to 3334 cm –1 , indicating a weakening of this bond and formation of new hydrogen bonding between Cr 2 O 7 2– and metal-bonded hydroxyl groups of CoAl-LDH (Figure S2, SI).…”

“…The powder X-ray diffraction (PXRD) pattern of CoAl-LDH samples in Figure a shows the classic nature of hydrotalcite materials, where diffraction peaks at 2θ of 11.81, 23.71, 34.66, and 39.21° are ascribed to 003, 006, 012, and 015 diffraction planes, respectively, matching with the hexagonal phase of (Co 4 Al 2 (OH) 12 CO 3 (H 2 O) 3 ) 0.5 (JCPDS card no. 97-017-2995) . The Co/Al molar ratio is obtained to be 3.76:1 using inductively coupled plasma (ICP), and the LDH formula is calculated to be [Co 0.79 Al 0.21 (OH) 2 (CO 3 ) 0.11 ]· m H 2 O. Chromium ion exchange in CoAl-LDH slightly shifts the (003) peak to lower 2θ, indicating an increase in interlamellar spacing from 7.48 to 7.62 Å due to the ion exchange of CO 3 2– with dichromate ions (Cr 2 O 7 2– ) (see zoomed PXRD in Figure S1a, Supporting Information, SI).…”

New Proposal in a Biorefinery Context: Recovery of Acetic and Formic Acids by Adsorption on Hydrotalcites

“…Previous studies reported that adsorption increases with increasing availability of active sites. 50,51,57 MG30c had fewer negative sites (1.677 mmol negative charge g −1 ) than MG63c and MG70c (3.636 and 2.924 mmol negative charge g −1 , respectively). A greater number of negative sites allows higher adsorption of compounds, which explains why MG63c adsorbed more AA and FA than the other hydrotalcites.…”

Adsorption studies and effect of heat treatment on porous glass microspheres

“…Although, higher surface area is one of the important parameters for an adsorbent, studies have reported that adsorption efficiency of an adsorbent is not only predominated by its surface area but also other factors such as surface chemistry and morphological features. [82][83][84][85] Yan et al studied successful adsorption of acid dyes by cetyltrimethyl ammonium bromide (CTMAB) modified organo-bentonite which had a surface area of 4.4 m 2 /g. 86 Deng et al reported removal of methylene blue dye using sulfuric acid treated cotton stalk (SCS) and phosphoric acid treated cotton stalk (PCS) with surface areas of 2.8 and 7.2 m 2 /g, respectively.…”