Abstract
In the present work, we proved the efficacy of cellulose citrate to remove methylene blue (MB) from artificially contaminated water. MB is a widely used dye, but because of its chemical aromatic structure, it is significantly stable with quite slow biodegradation, causing consequent serious health problems for people and significant environmental pollution. Cellulose citrate, the bio-adsorbent proposed and studied by us to remediate water polluted by MB, is produced by a green, cheap and fast procedure that makes use of two abundant natural products, cellulose and citric acid. The average of two citrate groups for each glucose unit of cellulose chains allows this material to have many carboxylic groups available for interaction with the cationic dye. The characterization was carried out through FT-IR, SEM, specific surface area, pore structure parameters and zeta potential. The negative value of the zeta potential at neutral pH is consistent with the affinity of this material for the adsorption of cationic compounds like MB. The activity of the adsorbent at different times, temperatures, pH and concentrations was investigated. The process followed monolayer adsorption typical of the Langmuir model, with a maximum adsorption capacity of 96.2 mg g−1, while for the kinetic studies the process followed a pseudo-second order model. The highest levels of adsorption were reported using solutions of dye with concentrations under 100 mg L−1. The adsorbent can be regenerated several times without a significant loss in the adsorption capacity, and it is not strongly affected by temperature and pH, giving rise to a simple and eco-sustainable procedure for water remediation. Therefore, we conclude that cellulose citrate can be considered as a promising bio-adsorbent for the removal of MB and other cationic pollutants from the environment.
Highlights
In recent years there has been increasing and widespread concern regarding environmental pollution and, the effort of the scienti c community to solve these problems has been remarkable
The adsorption properties of the cellulose citrate were tested on water arti cially contaminated by different concentrations of methylene blue (MB)
As already mentioned in the experimental section, initial tests were conducted on a solution of 25 mg of cellulose citrate (CC) added to 25 mL of MB solution (30 mg LÀ1)
Summary
Paper environment are not negligible, because its elevated quantity in wastewater induces a minor light absorption to detriment of the photosynthetic process of aquatic plants and signi cant toxicity for the aquatic organisms.[20,21] In spite of everything, methylene blue is surely one of the most used dye in textile industries and, for this reason, the developing of new strategies for the efficient removal from water effluents is still ongoing and of great interest.[22,23,24,25,26,27] The common methods for the removal of organic dyes include: chemical oxidation or reduction,[28] precipitation,[29] ion exchange,[30] electrolysis,[31] photo-catalytic processes,[32,33] membrane ltration,[34] ozonation,[35] degradation,[36] bio-sorption[37] and adsorption.[38,39] In particular, adsorption is one of the most used techniques because it relies on a simple mechanism, does not produce handling problems, and the process can be reversible.[40,41] Among adsorbents, activated carbon was employed over the years because of its efficacy for the removal of water and air pollutants, but it possesses many limitations as the production costs and the regeneration.[42,43] The conversion of waste into bio-adsorbent has a high economic value other to generate a very low impact on the environment with an easy biodegradability.[44,45] Inthapanya and co-workers investigated the removal of anionic acid green 25 using calcined oyster shells with a reported maximum adsorption capacity of 34.1 mg gÀ1.46 In another work Lin et al described a study on visible-lightdriven photocatalysis for the quantitative degradation of malachite green using a system with silver phosphate modi ed by MWCNTs and Cr-doped SrTiO3.47 Pure cellulose and/or cellulose-derived materials were deeply employed in the manufacturing of bio-adsorbent for pollutants removal, due to many advantages like the wide natural availability, chemical versatility, biodegradability, and precious chemical–physical properties.[48,49,50] The activity of microcrystalline cellulose for MB adsorption was thoroughly investigated, but it was proved to be efficient, in all the studies conducted to date, it is quite far from a quantitative removal.[51,52,53] On the other hand, in literature was reported that the functionalization of cellulosebased materials and biomass waste with carboxylic groups, enhances the adsorption capacity, even if performed through the use of hazardous materials like chloroacetic acid and methacrylic acid.[54,55,56] In this work, we have developed a green, cheap and fast method for the effective removal of MB to remediate polluted water by cellulose citrate (CC) that was obtained through a simple and eco-sustainable reaction between microcrystalline cellulose and citric acid. The characterization was carried out through FT-IR, SEM, speci c surface area, pore structure parameters and zeta potential
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