Enhancement of the Stability of Biosorbents for Metal-Ion Adsorption

Arabica-coffee and teobroma-cocoa agro-industrial waste biosorbents, for Pb(II) removal in aqueous solutions

Agro-industrial waste biosorbents of arabica-coffee (WCA) and theobroma-cocoa (WCT) have been characterized and tested to remove Pb(II) from aqueous media. The maximum adsorption capacity of WCA and WCT (q_max = 158.7 and 123.5 mg·g^-1, respectively) is comparable or even higher than for several other similar agro-industrial waste biosorbents reported in the literature. Structural and morphological characterization were performed by infrared spectrometry with Fourier transform (FT-IR), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), and charge measurements at the zero point charge (pH_PZC). Both biosorbents, WCA and WCT, show cracked surfaces with heterogeneous plates which ones include functional adsorption groups such as OH, C = O and C-O-C. Optimal Pb(II) adsorption occurs for a pH between 4 and 5 at [WCA] and [WCT] dose concentrations of 2 g·L^-1. We found that the adsorption process follows pseudo-second order kinetics with a rapid growth rate (almost six times larger for WCA than for WCT), basically controlled by the chemisorption process. The regeneration of both biosorbents was carried out in an eluent of 0.1M HNO₃ and they can be efficiently reused up to 5 times.

Effective removal of Cu(II) from aqueous solution over graphene oxide encapsulated carboxymethylcellulose-alginate hydrogel microspheres: towards real wastewater treatment plants

In the current study, the graphene oxide (GO) encapsulated carboxymethyl cellulose-Alginate (CMC-Alg) hydrogel microspheres were prepared via ionotropic gelation method and characterized using FTIR, TGA, SEM-EDS and surface charge by determining pH_pzc. The adsorption of Cu²⁺ ions from aqueous solution on the graphene oxide embedded CMC-Alg was studied under different experimental conditions, and the results showed that embedded beads had high adsorption capacity compared with pure CMC-Alg beads due to synergetic effect between functional groups GO and CMC-Alg matrix. Adsorption capacities at equilibrium were calculated experimentally as 22.10, 39.96, 41.72 and 64 mg/g for pure CMC-Alg, CMC-Alg/GO 1%, CMC-Alg/GO 3% and CMC-Alg/GO 5%, respectively. The adsorption kinetics were found to follow the pseudo-second-order, and the equilibrium data fitted well with the Langmuir adsorption isotherm. Moreover, the intraparticle diffusion model has been inspected pointing that the adsorption process was found to be sequence of surface adsorption and intraparticle diffusion (IPD). The results suggest that graphene oxide embedded CMC-Alg bead matrix can be efficiently used as an adsorbent for metal ions removal from wastewater.

Graphene oxide encapsulated polyvinyl alcohol/sodium alginate hydrogel microspheres for Cu (II) and U (VI) removal

In this work, a novel sodium alginate (SA)/polyvinyl alcohol (PVA)/graphene oxide (GO) hydrogel microspheres were prepared by a simple method. Sodium alginate was physically crosslinked by Ca²⁺; GO was encapsulated into the composite to strengthen the hydrogels; PVA played a significant role in well dispersing of GO in SA. The SA/PVA/GO (SPG) hydrogels were employed as an efficient adsorbent for removal of Cu (II) and U (VI) from aqueous solution. Batch experiments with the subject of the pH, initial metal ion concentration, competing ions and contact time were investigated. Structure characterization was successfully conducted by FTIR, SEM, EDX, BET and XPS. Furthermore, the sorption kinetics of Cu²⁺ and UO₂²⁺ followed pseudo-second order model and exhibited 3-stage intraparticle diffusion model. Equilibrium data were best described by Langmuir model and the obtained maximum adsorption capacities of SPG hydrogel microspheres for Cu²⁺ and UO₂²⁺ were 247.16 and 403.78 mg/g, respectively. The difference in adsorption capacity can be confirmed by the percentage of elements in EDX spectra and the intension of peak of elements in XPS spectra. The SPG sorbent exhibited excellent reusability after 5 adsorption-desorption cycles. All results suggested that the prepared adsorbents could be considered as effective and promising materials for removal of Cu (II) and U (VI) in wastewater.

Synthetically modified nano-cellulose for the removal of chromium: a green nanotech perspective

Existing processes for the decontamination of heavy metals from water are found to be cost-prohibitive and energy-intensive which is totally against the sustainable concept of development. Green nanotechnology for water purification for ecosystem management, agricultural and industry is an emerging as leading global priority and occupies better position over the current state of water purification. Herein, the diafunctionalised polyaniline modified nanocellulose composite sorbent (PANI-NCC) has been used to introduce amine and imine functionalities for the removal of trivalent and hexavalent chromium from water bodies. The fabricated nanobiomaterial has been authenticated by modern spectroscopic, microscopic techniques. The modified PANI-NCC is rod-like in shape, ~60 nm in size. The roughness and crystallinity index is also quantified and found to be 49.67 nm and 84.18%, respectively. The optimised experimental finding provides the efficient removal of trivalent [Cr(III)] (47.06 mg/g; 94.12%) and hexavalent [Cr(VI)] (48.92 mg/g; 97.84%) chromium from synthetic waste water. The fabricated nano biosorbent is deemed to be a potent biosorbent for technological development to remove the toxic metals in the real environmental water samples.