Adsorption of Phosphate Dianions by Hybrid Inorganic–Biopolymer Polyelectrolyte Complexes: Experimental and Computational Studies

Abstract

Hybrid inorganic–biopolymer polyelectrolyte complexes (HIB-PECs) consisting of chitosan, alginate, and an aluminum-based cross-linking agent were prepared at variable chitosan and alginate mass ratios. IR spectral results indicate that chitosan and alginate undergo PEC formation according to the spectral shifts of the −NH3 + and COO– groups for chitosan and alginate, respectively. Evidence of Al–O–R (where R = alkyl group) and Al–OH bonds are supported by XPS, PXRD, and NMR spectra. Computational studies provide additional support that aluminum undergoes cross-linking with the carboxylate groups of alginate of the PEC. SEM and pHpzc results provide support of variable product morphology and surface charge for the HIB-PECs over the pristine biopolymers. Equilibrium adsorption studies of the hydrogen phosphate dianion at pH 8.5 reveal that chitosan with alginate at a 1:1 (w/w) ratio afforded an HIB-PEC with an optimal adsorption capacity (Q m = 152 ± 44 mg/g). The Sips isotherm model accounts for the adsorption data, where the uptake parameters indicate a heterogeneous adsorbent surface with physisorption uptake properties. Increased temperatures led to reduced uptake capacity of the HIB-PECs, where competitor anion species had no apparent effects. Computational studies revealed that the −OH sites of the aluminum complex in the HIB-PECs serve as the preferred active site for phosphate anion uptake. Regeneration of the HIB-PECs over four adsorption–desorption cycles did not show any attenuation of the adsorption capacity. This study presents a first example of the application of HIB-PECs for the adsorption of phosphate species in aqueous solution, where the computational and experimental studies provided complementary support that the −OH sites of the aluminum complex serve as the key active adsorption site for the phosphate anion species.

Sequestration of Sulfate Anions from Groundwater by Biopolymer-Metal Composite Materials

“…The thermal decomposition behavior of chitosan, alginate, CCu1 and the ternary composite materials are illustrated in Figure 3 and Figure S2a–f . These profiles reveal two or three thermal events that vary across a temperature range up to 400 °C, in parallel agreement with a related study [ 73 ]. In general, the first thermal event occurs between 36 to 120 °C that relates to loss of bound surface water and/or entrapped water from the composite network [ 74 ].…”

Counterion Effects in Metal Hybrid Biopolymer Materials for Sulfate Adsorption: An Experimental and Computational Study

“…Although aluminum hydroxide has experienced attention for pollutant removal, such Al-based materials require modification for enhanced uptake characteristics . Biopolymer composites that contain chitosan and alginate were reported, , which employ Lewis acids (e.g., metal cations) to enable the formation of stable ternary metal composites (TMCs). Biopolymer-based TMCs can be prepared as solid-phase adsorbents with promising anion adsorption properties. ,− Recently, Udoetok et al .…”

Lower Critical Solution Temperature-Driven Catch and Release of Perfluoroalkyl Substances from Water: Remediation and Sampling

“…A cross-linked P-NIPMAM adsorbent (20 mm × 20 mm, thickness = 100 μm) was submerged in a PFOA aqueous solution (concentration, C o = 0.6 mg mL –1 ) for 10 h at a temperature of 75 °C (>LCST ≈73.9 °C). Note that the thickness of 100 μm is comparable to that of the adsorbents in PFAS-adsorbing devices (e.g., Polar Organic Chemical Integrative Sampler modules) that are currently in use. , Figure c demonstrates the value of α which is given by α = ( C o – C a, t =10h ) V / m . Here, C a, t =10h is the concentration of PFOA at t = 10 h. V and m are the volume of the PFOA solution (20 mL) and the mass of dry P-NIPMAM (100 mg), respectively.…”

“…42,43 Figure 2c demonstrates the value of α which is given by α = (C o − C a,t=10h )V/m. 44 Here, C a,t=10h is the concentration of PFOA at t = 10 h. V and m are the volume of the PFOA solution (20 mL) and the mass of dry P-NIPMAM (100 mg), respectively. High-performance liquid chromatography−mass spectrometry (HPLC-MS) was utilized to measure C a,t (Experimental Section).…”