Adsorption and identification of traces of dyes in aqueous solutions using chemically modified eggshell membranes

Highly Porous Hydroxyapatite/Graphene Oxide/Chitosan Beads as an Efficient Adsorbent for Dyes and Heavy Metal Ions Removal

Dye and heavy metal contaminants are mainly aquatic pollutants. Although many materials and methods have been developed to remove these pollutants from water, effective and cheap materials and methods are still challenging. In this study, highly porous hydroxyapatite/graphene oxide/chitosan beads (HGC) were prepared by a facile one-step method and investigated as efficient adsorbents. The prepared beads showed a high porosity and low bulk density. SEM images indicated that the hydroxyapatite (HA) nanoparticles and graphene oxide (GO) nanosheets were well dispersed on the CTS matrix. FT-IR spectra confirmed good incorporation of the three components. The adsorption behavior of the obtained beads to methylene blue (MB) and copper ions was investigated, including the effect of the contact time, pH medium, dye/metal ion initial concentration, and recycle ability. The HGC beads showed rapid adsorption, high capacity, and easy separation and reused due to the porous characteristics of GO sheets and HA nanoparticles as well as the rich negative charges of the chitosan (CTS) matrix. The maximum sorption capacities of the HGC beads were 99.00 and 256.41 mg g⁻¹ for MB and copper ions removal, respectively.

The use of eggshell membrane for the treatment of dye-containing wastewater: Batch, kinetics and reusability studies

The worldwide consumption of eggs is very high, leading to about 250,000 tons of eggshell membrane (ESM) waste annually. The present research thus investigated the potential use of ESM as an inexpensive and abundant adsorbent for Reactive Red 120 (RR120) in aqueous solutions, a widespread hydrophilic azo dye used in the textile industry. The chemical structure and morphology of ESM were characterized using various spectroscopic methods, including scanning electron microscopy, Fourier transform infrared spectroscopy, and elemental analysis. It was found that natural ESM has a porous structure and surface functional groups that are suitable for the adsorption of the target molecules. The impact of the operating conditions, including the variation in the pH and temperature, on the RR120 sorption capacity and mechanisms of ESM was also analyzed. The maximum monolayer adsorption ability of ESM for RR120 was found to be 191.5 mg/g at 318 K, and the sorption process was spontaneous and endothermic. The adsorption of RR120 onto ESM was significantly influenced by the solution pH and the use of NaOH as eluent, indicating that the driving force for this adsorption was electrostatic attraction. Subsequent desorption experiments using 0.1 M NaOH resulted in satisfactory recovery efficiency. Kinetic, isothermic, and thermodynamic analysis was also conducted to support the experimental findings. The experimental results for the adsorption kinetics of ESM were fitted by a pseudo-second-order model. In conclusion, ESM has the potential to be utilized as an eco-friendly and cost-effective adsorbent for the removal of RR120 from aqueous solutions.

Advances in application of cotton-based adsorbents for heavy metals trapping, surface modifications and future perspectives

Cotton-based adsorbents (CBAs) are promising materials for combating the problem of heavy metal pollution of environmental waters. This is ascribed to the low cost, abundance, biodegradability and efficiency of CBAs. Herein we review the adsorption of heavy metals (HMs) onto CBAs. We found that several surface modifications were employed to improve the efficiency of the CBAs. These modifications were effected via thermal, physical and chemical means to obtain activated carbons, biochars, ionic liquids, aerogels, hydrogels, chitosans and nanoparticle-derived CBAs. The CBAs exhibited maximum HMs uptake as low as 0.002 mg/g to as high as 505.6 mg/g. Although, the cotton-derived activated carbons and biochars exhibited enhanced HM uptake from that of the unmodified CBAs, they were less efficient than CBAs modified by other methods. Recent chemical, ionic liquid, chitosan and nano-derived CBAs were the most efficient, with high uptake and fast kinetic removal. However, the nanoparticle-based adsorbents are preferred to the chemically modified forms, due to the possibility of secondary pollution and the noxious effect of the latter to the environment. Findings showed that chemical treatment produced CBAs most efficient for As(V), Pb(II) and Fe(III), while ionic liquid CBA was more efficient for Cu(II) and Ni(II). Nano-based treatment was suitable for the uptake of Co(II), Zn(II), Pb(II) and Cd(II), while the chitosan based adsorbent was viable for Hg(II). Isotherm and kinetic evaluation of CBAs mostly conformed to the Langmuir and pseudo-second order models, respectively. Spontaneous adsorption of HMs onto CBAs was deduced from thermodynamic analysis, with endothermic and exothermic characteristics. Over 88% desorption of HMs was obtained from the CBAs studied with good average reusability from 3 to 20 cycles. We also discussed the directions for future research.

Synthesis of silver nanoparticles utilizing various biological systems: mechanisms and applications-a review

The evolving technology of nanoparticle synthesis, especially silver nanoparticle (AgNPs) has already been applied in various fields i.e., electronics, optics, catalysis, food, health and environment. With advancement in research, it is possible to develop nanoparticles of various size, shape, morphology, and surface to volume ratio utilizing biological systems. A number of different agents and methods can be employed to develop choice based AgNPs using algae, plants, fungi and bacteria. The use of plant extracts to produce AgNPs appears to be more convenient, as the method is simple, environmental friendly and inexpensive, also requiring a single-step. The microbial synthesis of AgNps showed intracellular and extracellular mechanisms to reduce metal ions into nanoparticles. Studies have shown that different size (1-100 nm) and shapes (spherical, triangular and hexagonal etc.) of nanoparticles can be produced from various biological routes and these diverse nanoparticles have various functions and usability i.e., agriculture, medical-science, textile, cosmetics and environment protection. The present review provides an overview of various biological systems used for AgNP synthesis, its underlying mechanisms, further highlighting the current research and applications of variable shape and sized AgNPs.