Saeed Ahmed

The escalating global water pollution crisis demands innovative and sustainable remediation strategies. This review critically assesses the application of nanocomposite beads as advanced adsorbents for efficiently removing diverse contaminants from aqueous environments. Nanocomposite beads, engineered with tailored physicochemical properties, offer significant advantages over conventional adsorbents due to their high specific surface area, tunable porosity, and adaptable surface functionalities. A comprehensive review summarises the nanocomposite bead-like layered double hydroxides (LDHs), metal–organic frameworks (MOFs), metal oxides, and carbonaceous materials. The review elucidates the structure–property relationships governing the adsorption performance of these nanocomposites. A detailed analysis of the underlying adsorption mechanisms is presented, encompassing physisorption (e.g., van der Waals interactions), chemisorption (e.g., covalent bonding, complexation), electrostatic interactions, ion exchange, and surface complexation. Furthermore, this review addresses the challenges of implementing nanocomposite beads in large-scale water treatment systems. Moreover, this study also provides a comprehensive roadmap for researchers working towards developing sustainable and cost-effective solutions for water purification using nanocomposite adsorbents.

Pharmaceuticals in polluted water can harm humans, animals, and marine life. Pharmaceuticals undergo degradation, producing secondary products that are more toxic. Their infiltration can become life-threatening rather than life-saving if they are not properly disposed of. Among various processes such as membrane filtration, advanced oxidation processes, and biodegradation, adsorption is considered the most appropriate for efficiently removing pharmaceuticals from water. This review summarizes different adsorbents and recent advances to enhance the adsorption capacity of the adsorbents, including carbon-based material, zeolites, metal-organic frameworks, and polymers. Every adsorbent is evaluated based on different parameters like removal capacity, removal efficiency, pH, temperature, and mechanism of action. The parameters like pH range and temperature depend on the adsorbent–adsorbate system and the experimental conditions. There was a wide variation in removal efficiencies: 28%–99.7% for carbon-based adsorbents, 37%–100% for zeolites, 86%–99.3% for metal-organic frameworks, and 70%–98.2% for polymers. The possible interactions between pharmaceuticals and adsorbents are included for further improvements to increase the adsorption. The outcome of this study highlighted the use of adsorbents and demonstrated how their modification can improve the adsorption of pharmaceuticals from water bodies.

A series of porous silica materials coated with honeycomb-like magnesium silicate were prepared under hydrothermal conditions, using natural one-dimensional porous attapulgite as the template and a silicon source with different Mg/Si ratios, by adjusting the amount of MgCl₂⋅6H₂O and the attapulgite precursor and regulating pH. The influence of the Mg/Si ratios was carefully investigated on morphology, pore structure, and related adsorption actions toward methylene blue. The Langmuir isotherm and pseudo-second-order kinetic models were used to explain the adsorption behavior of methylene blue. The synthesized composite with the lowest magnesium content displayed the highest removal capability of 166.67 mg/g for methylene blue, with a zeta potential of −18.18 mV, a specific surface area of 310.4 m²/g, and an average pore size of 3.7 nm. The removal result was the synergetic adsorption between porous magnesium silicate grown on the surface and the rest of the silica, further indicating that the attapulgite is available as a silicon source and a rod-shaped template for magnesium silicate.

The continuous discharge of organic dyes into freshwater resources poses a long-term hazard to aquatic life. The advanced oxidation Fenton process is a combo of adsorption and degradation of pollutants to detoxify toxic effluents, such as anti-bacterial drugs, antibiotics, and organic dyes. In this work, an activated attapulgite clay-loaded iron-oxide (A-ATP@Fe₃O₄) was produced using a two-step reaction, in which attapulgite serves as an enrichment matrix and Fe₃O₄ functions as the active degrading component. The maximum adsorption capacity (q_t) was determined by assessing the effect of temperature, pH H₂O₂, and adsorbent. The results showed that the A-ATP@Fe₃O₄ achieves the highest removal rate of 99.6% under optimum conditions: 40 °C, pH = 3, H₂O₂ 25 mM, and 0.1 g dosage of the composite. The dye removal procedure achieved adsorption and degradation equilibrium in 120 and 30 min, respectively, by following the same processes as the advanced oxidation approach. Catalytic activity, kinetics, and specified surface characteristics suggest that A-ATP@Fe₃O₄ is one of the most promising candidates for advanced oxidation-enrooted removal of organic dyes.

Attapulgite (APT) is widely used in wastewater treatment due to its exceptional adsorption and colloidal properties, as well as its cost-effectiveness and eco-friendliness. However, low-grade APT generally limits its performance. Here, a colloid mill-assisted ultrasonic-fractional centrifugal purification method was developed to refine low-grade APT. This process successfully separated and removed impurity minerals such as quartz and dolomite from the raw ore, resulting in a refined APT purity increase from 16.9% to 60% with a specific surface area of 135.5 m²∙g⁻¹. Further modifying of the refined APT was carried out through the hydrothermal method using varying dosages of cetyltrimethylammonium chloride (CTAC), resulting in the production of four different APT adsorbents denoted as QAPT-n (n = CTAC mole number) ranging from 0.5 to 5 mmol. Using Congo red (CR) as the target pollutant, the QAPT-5 sample exhibited the best adsorption capacity with the maximum quantity of 1652.2 mg∙g⁻¹ in a neutral solution at 30 °C due to the highest surface charge (zeta potential = 8.25 mV). Moreover, the QAPT-5 pellets (~2.0 g adsorbent) shaped by the alginate-assisted molding method removed more than 96% of 200 mL aqueous solution containing 200 mg∙L⁻¹ CR and maintained this efficiency in 10 adsorption–elution cycles, which exhibited the promising practical application.