Enhanced removal of methylene blue from wastewater by alginate/carboxymethyl cellulose-melamine sponge composite

Synthesis, characterization, and photocatalytic activity of a carboxymethyl cellulose sodium-based hybrid material for efficient degradation of hexavalent chromium

Conventional water treatment technologies often struggle to eliminate Cr(VI) effectively. Consequently, developing efficient and cost-effective photocatalysts for degrading Cr(VI) has emerged as a promising approach to environmental remediation. In this study, two novel cellulose-based photocatalytic hydrogel materials, designated CF and CFS, were synthesized by cross-linking varying concentrations of Fe(III) and Fe(III) + sodium citrate (SC) with sodium carboxymethyl cellulose (CMC), marking their first application in the photocatalytic reduction of Cr(VI) in aquatic environments. Photocatalytic degradation experiments revealed that the Fe(III) concentration was 0.3 M with a Fe(III): SC molar ratio of 2:1, 150 mg/L Cr(VI) could be 100 % degraded within 90 min. The microscopic structure and chemical properties of photocatalysts were thoroughly characterized, and the results confirmed the successful cross-linking of CMC with Fe(III) and Fe(III) + SC. Optical and electrochemical tests indicated that CFS exhibited a broader visible-light absorption range, a narrower band gap, and significantly improved separation and transfer of photogenerated carriers. Furthermore, CFS had a highly photochemically active Fe(III)-SC complex, which established a Fe(III)/Fe(II) cycling process via the metal-ligand-charge transfer (MLCT) pathway, leading to the rapid degradation of Cr(VI). CF and CFS still had good stability and reusability after five cycles. Therefore, this study provides an approach for removing Cr(VI) contaminants.

Effect of a sodium carboxymethyl cellulose composite hydrogel on tobacco growth and development under drought stress

In order to promote the growth and development of tobacco and reduce the adverse effects of drought on tobacco, acrylamide/sodium carboxymethyl cellulose/modified biochar hydrogel (AM/CMC/MB) was prepared by crosslinking polymerization reaction. The structural characteristics of the hydrogel were comprehensively analysed using Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Additionally, the water absorption capacity of the hydrogel was quantitatively evaluated. Furthermore, this study investigated the efficacy of AM/CMC/MB hydrogel in promoting the growth and development of potted tobacco seedlings under drought stress conditions. The results showed that the equilibrium solubility of AM/CMC/MB hydrogel was increased by 74.83 % and the diffusion process of water molecules followed the non-Fickian diffusion law compared with commercially available water retention agents. The openness of stomata of tobacco seedlings and the SPAD values were improved. The MDA (Malondialdehyde) content of tobacco seedlings was reduced by 47.50 %, CAT (Antioxidant enzymes catalase) and POD (Peroxidase) activities were increased by 198.15 % and 198.23 %, respectively. The total amount of metabolites detected after drought in tobacco seedlings supplemented with hydrogel AM/CMC/MB was increased by 50.33 % as compared to the control. This study provides a basis for the use of AM/CMC/MB as a water retention agent for tobacco growth and development.

Highly-selective and well-effective removal of cesium ions by segregative titanium-ferrocyanide/chitosan melamine sponge composite

Selectively and efficiently removing Cs is of great urgency and challenge for the treatment of radioactive wastewater. In this work, titanium-ferrocyanide/chitosan melamine sponge composite (TFCM) was synthesized by cross-linking and titanium-doping strategy, and employed to remove Cs+ from water. The obtained TFCM exhibited excellent adsorption performance for Cs+, due to its porous and 3D skeleton structure. The TFCM demonstrated a broad range of pH (pH = 3-11) suitability and high removal ratio of Cs+. The adsorption behavior of TFCM on Cs+ conformed to the Langmuir adsorption process and pseudo-second-order kinetics model. Remarkably, TFCM displayed a high selectivity in Cs+ adsorption with the presence of other cationic (K+, Na+, Ca2+, Mg2+). TFCM could easily be separated from water because of loading on the melamine sponges. Besides, the TFCM could maintain more than 78.1 % removal ratio of Cs+ after five adsorption-desorption cycles. Furthermore, the concentration of Cs+ could decrease to 10 μg/L from 20 mg/L with a prominent removal ratio of 99.95 %. Characterization results revealed that the adsorption process of Cs+ by TFCM was dominated by ion-exchange. In summary, the TFCM is a high selectivity, efficiently and easily separable adsorbent with excellent application prospects for removing Cs from radioactive wastewater.

Alginate-Based Hydrogel Bead Reinforced with Montmorillonite Clay and Bacterial Cellulose-Activated Carbon as an Effective Adsorbent for Removing Dye from Aqueous Solution

According to environmental concerns related to water pollution, this study aims to develop a novel hydrogel bead as a biocompatible and efficient adsorbent by integrating bacterial cellulose-activated carbon (BCAC) and montmorillonite (MT) in alginate hydrogel (ALG). The ionotropic gelation method was applied to the fabrication of BCAC/MT/ALG hydrogel beads. The BCAC/MT/ALG hydrogel bead exhibited significantly higher tensile strength, Young's modulus, and thermal stability, with ~1.4 times higher adsorption uptake of methylene blue (MB) from aqueous solution as compared to the pristine ALG bead. The textural properties, including specific surface area and porosity, were beneficial to accommodate the size of cationic MB as the target molecule. This resulted in a remarkable MB adsorption uptake of 678.2 mg/g at pH 7 and 30 °C. The adsorption isotherm showed the best fit for the nonlinear Redlich-Peterson isotherm model. Experimental adsorption data were well-described by the pseudo-second order kinetic model, with R2 values reaching 0.997. In addition, the adsorbent bead demonstrated easy regeneration with high reusability with approximately 75% of MB removal after being used for six cycles. Therefore, BCAC/MT/ALG bead represents an eco-friendly, cost-effective, and highly efficient adsorbent for MB removal from water and could potentially be used for removal of a wide range of cationic dye pollutants from wastewater.

One stone, two birds: An eco-friendly aerogel based on waste pomelo peel cellulose for the efficient adsorption of dyes and heavy metal ions

To achieve the objective of "waste control by waste", in this study, a green aerogel adsorbent comprised of pomelo-peel cellulose and sodium alginate (PCC/SA) was prepared through dual-network crosslinking. The resulting 3D hierarchical porous structured PCC/SA aerogel exhibited good structural stability, and kept the morphological integrity during 10 days in a wide pH range (2-10), suggesting its potential for recycling in diverse complex environments. Besides, the superior adsorption capacities for methylene blue (MB) and Cu(II) were observed, with the qm values and adsorption equilibrium times were recorded to be 1299.59 mg/g (300 min) and 287.55 mg/g (120 min), correspondingly. Furthermore, the favorable reusability of the PCC/SA aerogel was also demonstrated, with the removal efficiency for MB remaining almost unchanged (about 94 %) after 10 adsorption-desorption cycles, while there was a slight reduction for Cu(II) from 85.28 % to 72.47 %. XPS and FTIR analysis revealed that electrostatic attraction, hydrogen bonding, cation exchange and coordination were the major adsorption mechanisms. Importantly, the PCC/SA aerogel can be naturally degraded in soil within 10 weeks. Therefore, the as-prepared aerogel bead derived from pomelo peel shows great promise as an adsorbent for wastewater treatment containing dye and heavy metal ions.

A novel sponge composite of chitosan-sodium tripolyphosphate-melamine for anionic dye Orange II removal

Since the potential carcinogenic, toxic and non-degradable dyes trigger serious environmental contamination by improper treatment, developing novel adsorbents remains a major challenge. A novel high efficiency and biopolymer-based environmental-friendly adsorbent, chitosan‑sodium tripolyphosphate-melamine sponge (CTS-STPP-MS) composite, was prepared for Orange II removing with chitosan as raw material, sodium tripolyphosphate as cross-linking agent. The composite was carefully characterized by SEM, EDS, FT-IR and XPS. The influence of crosslinking conditions, dosage, pH, initial concentration, contacting time and temperature on adsorption were tested through batch adsorption experiments. CTS-STPP-MS adsorption process was exothermic, spontaneous and agreed with Sips isotherm model accompanying the maximum adsorption capacity as 948 mg∙g-1 (pH = 3). Notably, the adsorption performance was outstanding for high concentration solutions, with a removal rate of 97 % in up to 2000 mg∙L-1 OII solution (100 mg sorbent dosage, 50 mL OII solution, pH = 3, 289.15 K). In addition, the adsorption efficiency yet remained 97.85 % after 5 repeated adsorption-desorption cycles. The driving force of adsorption was attributed to electrostatic attraction and hydrogen bonds which was proved by adsorption results coupled with XPS. Owing to the excellent properties of high-effective, environmental-friendly, easy to separate and regenerable, CTS-STPP-MS composite turned out to be a promising adsorbent in contamination treatment.

Adsorption performance of mineral-carbon adsorbents derived from coal gasification fine ash: Prepared via low-temperature alkali fusion method

To address the solid waste challenges associated with coal gasification fine ash, this study conducted a low-temperature alkali fusion de-ashing treatment to transform coal gasification fine ash into mineral-carbon adsorbent. The preparation process was simplified without grinding, carbonization and high-temperature (500-800 °C) activation treatment. The results demonstrate a positive linear correlation between the ash removal rate of the samples (measured during the preparation process, i.e., low-temperature alkaline fusion treatment of coal gasification fine ash) and their maximum equilibrium adsorption capacity for methylene blue. For the samples with an ash removal rate of 95.71 %, which exhibit a maximum adsorption capacity of 161.36 mg/g for methylene blue. The adsorption behavior of methylene blue on mineral-carbon adsorbent was a monolayer adsorption on the surface of homogeneous medium, involving both physical and chemical adsorption. The main adsorb rate-controlling steps for the samples with ash removal rates of 27.91-59.33 % and 95.71 % were the intra particle diffusion process and the liquid film diffusion process, respectively. The adsorption mechanism of methylene blue on the surface of mineral-carbon adsorbent involved electrostatic attraction and hydrogen bonding. The aforementioned results demonstrated the potential of coal gasification fine ash as an adsorbent material, providing new options for promoting the resource utilization and high-value applications of coal gasification fine ash.