Phosphorylated chitin from shrimp shell waste: A robust solution for cadmium remediation

In this work, chitin (CT) was isolated from shrimp shell waste (SSW) and was then phosphorylated using diammonium hydrogen phosphate (DAP) as a phosphorylating agent in the presence of urea. The prepared samples were characterized using Scanning Electron Microscopy (SEM) and EDX-element mapping, Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA/DTG), conductometric titration, Degree of Substitution (DS) and contact angle measurements. The results of characterization techniques reveal the successful extraction and phosphorylation of chitin. The charge content of the phosphorylated chitin (P-CT) was 1.510 mmol·kg-1, the degree of substitution of phosphorus groups grafted on the CT surface achieved the value of 0.33. The adsorption mechanisms appeared to involve electrostatic attachment, specific adsorption (CdO or hydroxyl binding), and ion exchange. Regarding the adsorption of Cd2+, the effect of the adsorbent mass, initial concentration of Cd2+, contact time, pH, and temperature were studied in batch experiments, and optimum values for each parameter were identified. The experimental results revealed that P-CT enhanced the Cd2+ removal capacity by 17.5 %. The kinetic analyses favored the pseudo-second-order model over the pseudo-first-order model for describing the adsorption process accurately. Langmuir model aptly represented the adsorption isotherms, suggesting unimolecular layer adsorption with a maximum capacity of 62.71 mg·g-1 under optimal conditions of 30 °C, 120 min, pH 8, and a P-CT dose of 3 g·L-1. Regeneration experiments evidenced that P-CT can be used for 6 cycles without significant removal capacity loss. Consequently, P-CT presents an efficient and cost-effective potential biosorbent for Cd2+ removal in wastewater treatment applications.

Lignin-functionalized cobalt for catalytic reductive degradation of organic dyes in simple and hybrid binary systems

To fulfill the unprecedented valorization approaches for lignocellulose, this work focuses on the potential of lignin-derived catalytic systems for bio-remediation, which are natural materials perceived to address the increased demand for eco-conscious catalyzed processes. A useful lignin-functionalized cobalt (Lig-Co) catalyst has been prepared, well-characterized and deployed for the catalyzed reducing decomposition of stable harmful organic pollutants such as methylene blue (MB) and methyl orange (MO), in simple and binary systems. The multifunctional character of lignin and the presence of various active sites can promote effectively loaded metal nanoparticles (NPs). Considerably, optimizing detoxification tests showed that the uncatalyzed use of NaBH4 as a reductive agent led to an incomplete reduction of organic contaminants over a long period of up to 65 min. Interestingly, Lig-Co catalyst exhibited a high reduction rate and turnover frequency of up to 99.23% and 24.12 min-1 for MB, respectively, while they reached 99.25% and 26.21 min-1 for MO at normal temperature. Kinetically quick catalytic reaction was also demonstrated for the hybrid system, in which the rate constant k was 0.175 s-1 and 0.165 s-1 for MB and MO, respectively, within a distinctly low reaction time of around 120 s. The reproducibility of the Lig-Co catalyst induces a desirable capacity to reduce stable dyes present simultaneously in the binary system, with 6 successive catalytic runs and over 80% of activity retained. Such robust findings underline the considerable interest in developing future lignin-mediated catalytic transformations and upscaling biomass-derived products, to meet the growing demand for sustainable and eco-friendly alternatives in various industries.

Bio-based functionalized adsorptive polymers for sustainable water decontamination: A systematic review of challenges and real-world implementation

The overwhelming concerns of water pollution, industrial discharges and environmental deterioration by various organic and inorganic substances, including dyes, heavy metals, pesticides, pharmaceuticals, and detergents, intrinsically drive the search for urgent and efficacious decontamination techniques. This review illustrates the various approaches to remediation, their fundamentals, characteristics and demerits. In this manner, the advantageous implementation of nature-based adsorbents has been outlined and discussed. Different types of lignocellulosic compounds (cellulose, lignin, chitin, chitosan, starch) have been introduced, and the most used biopolymeric materials in bioremediation have been highlighted; their merits, synthesis methods, properties and performances in aqueous medium decontamination have been described. The literature assessment reveals the genuine interest and dependence of academic and industrial fields to valorize biopolymers in the adsorption of various hazardous substances. Yet, the full potential of this approach is still confined by certain constraints, such as the lack of reliable, substantial, and efficient extraction of biopolymers, as well as their modest and inconsistent physicochemical properties. The futuristic reliance on such biomaterials in all fields, rather than adsorption, is inherently reliable on in-depth investigations and understanding of their features and mechanisms, which can guarantee a real-world application and green technologies.

Adsorption of cationic and anionic dyes onto coffee grounds cellulose/sodium alginate double-network hydrogel beads: Isotherm analysis and recyclability performance

This work describes the preparation of new eco-friendly adsorbents with a simple method. Gel beads of coffee grounds cellulose (CGC) and sodium alginate (SA) were prepared for wastewater treatment. Upon their synthesis, the physicochemical properties, performances and efficiency were analyzed by means of various structural and morphological characterizations. Kinetic and thermodynamic adsorption approaches evaluated the removal capacity of these beads which reached equilibrium in 20 min for Methylene Blue (MB) and Congo Red (CR). Also, the kinetics shows that the results can be explained by the pseudo-second-order model (PSO). Furthermore, the isotherm assessments showed that Langmuir-Freundlich can fit the adsorption data of both contaminants. Accordingly, the maximum adsorption capacities reached by the Langmuir-Freundlich model are 400.50 and 411.45 mg/g for MB and CR, respectively. It is interesting to note that the bio-adsorption capabilities of MB and CR on bead hydrogels decreased with temperature. Besides, the results of the thermodynamic study evidenced that the bio-adsorption processes are favorable, spontaneous and exothermic. The CGC/SA gel beads are therefore outstanding bio-adsorbents, offering a great adsorptive performance and regenerative abilities.