Adsorption of lead ions by activated carbon doped sodium alginate/sodium polyacrylate hydrogel beads and their in-situ recycle as sustainable photocatalysts

Valorization of carbon soot ash for the selective capture of lead ions from industrial waste water-A waste to resource approach

Landfills are struggling to accommodate the increasing amounts of carbon soot ash waste from oil refineries. Due to extensive industrial productions, large quantities of lead ions are released into the environment, which not only pollutes the environment but also affects flora and fauna. In this work, these urgent environmental issues will be tackled by studying the use of modified carbon soot ash for specific heavy metal adsorption. Carbon soot ash modified with chemical leaching and physical ball-milling was loaded onto the surface of graphene oxide. This adsorbent was found to selectively adsorb and remove toxic lead ions (>99%) from a mixed heavy metal solution. The adsorption efficiency was found to increase with temperature (20-60 °C) and pH (2-8). Langmuir isotherm and pseudo-second order kinetics were found to fit the adsorption process through curve fitting, where the adsorbent reached a maximum capacity of 194.55 mg/g. Potential mechanisms for lead adsorption and metal specificity are also discussed here. This work aligns with the waste-to-resource pathway, where waste carbon soot ash is diverted from landfilling and is formulated as a specific heavy metal adsorbent, that shows promise for environmental remediation.

Porous sodium alginate/cellulose nanofiber composite hydrogel microspheres for heavy metal removal in wastewater

High adsorption capacity, high adsorption rate and reusable adsorbents are urgent needed for removing heavy metals from wastewater. In this study, porous sodium alginate/cellulose nanofiber (SA/CNF) composite hydrogel microspheres were prepared by combining sodium alginate with cellulose nanofibers by microfluidics technology and adding polyethylene glycol (PEG) as pore making agent. The SA/CNF composite hydrogel microspheres could efficiently adsorb heavy metals (Pb2+, Cu2+ and Cd2+) in wastewater. The influencing factors of adsorption process, including pH, temperature, initial concentration, coexisting ions and aquatic environments, were systematically discussed. The adsorption process was more consistent with Langmuir isotherm model and pseudo-second-order model in batch system, indicating the adsorption process was mainly chemical adsorption. The adsorption capacity to Pb2+ obtained by Langmuir model was as high as 544.66 mg/g at 20 °C. Fixed-bed column adsorption experiments demonstrated the excellent performance of the as-prepared SA/CNF microspheres for treatment of the flowing wastewater in a column system. Overall, a highly practical adsorption process based on hydrogel adsorbents was developed for the removal of heavy metals from actual wastewater.

Preparation of Magnetic Spongy Porous Carbon Skeleton Materials for Efficient Removal of BTEX

Magnetic polymer microspheres have been extensively utilized as separable and highly efficient adsorbents in wastewater treatment. In this study, a series of novel magnetic spongy porous carbon skeleton materials (Mag-SPCS) have been designed and synthesized by acetonitrile suspension precipitation polymerization, which combines the advantages of the acetonitrile precipitation method and the suspension polymerization method. It was demonstrated that the transformation of the material morphology from microspheres to a porous sponge was achieved by a gradual decrease in the usage amount of ethylene glycol. After N,N-dimethyloctadecylamine (C18) was grafted onto the Mag-SPCS materials, the C18-Mag-SPCS materials with a superhigh saturation adsorption capacity and superfast adsorption efficiency were used for the removal of BTEX (toluene, benzene, and para-xylene) in wastewater. Subsequently, the adsorption properties of the composites with different morphologies were evaluated, and the effect of the usage amount of C18 on the adsorption properties of the C18-Mag-SPCS was further investigated. The maximum adsorption capacities of C18-Mag-SPCS for benzene, toluene, and para-xylene were 714.84, 564.32, and 394.48 mg/g, respectively. The adsorption process was conducted in accordance with the proposed secondary and Langmuir models. Finally, the FTIR, XPS, and XRD characterization results before and after adsorption demonstrated that the adsorption mechanism of toluene onto C18-Mag-SPCS was primarily hydrogen bonding, π-π stacking, and van der Waals forces. These findings of the study indicate that the composite material exhibits an ultrahigh saturation adsorption capacity and ultrafast adsorption efficiency, thereby confirming its considerable potential for application in wastewater treatment.

Advances in Hydrogels Research for Ion Detection and Adsorption

The continuing development of heavy industry worldwide has led to an exponential increase in the amount of wastewater discharged from factories and entering the natural world in the form of rivers and air. As the top of the food chain in the natural world, toxic ions penetrate the human body through the skin, nose, and a few milligrams of toxic ions can often cause irreversible damage to the human body, so ion detection and adsorption is related to the health and safety of human beings. Hydrogel is a hydrophilic three-dimensional reticulated polymer material that first synthesized by Wichterle and Lim in 1960, which is rich in porous structure and has a variety of active adsorption sites as a new type of adsorbent and can be used to detect ions through the introduction of photonic crystals, DNA, fluorescent probe, and other materials. This review describes several synthetic and natural hydrogels for the adsorption and detection of ions and discusses the mechanism of ion adsorption by hydrogels, and provide a perspective for the future development.

Designing of a cellulose-based ion-imprinted biosorbent for selective removal of lead (II) from aqueous solutions

Developing an effective adsorbent for Pb2+ removal from wastewater has huge economic and environmental implications. Adsorbents made from cellulosic materials that have been modified with certain chelators could be used to get rid of metal cations from aqueous solutions. However, their selectivity for specific metals remains very low. Here, we describe the synthesis of 4-(2-pyridyl)thiosemicarbazide (PTC) hydrazidine-functionalized cellulose (Pb-PTC-CE), a polymer imprinted with Pb2+ ions that may be used to remove Pb2+ ions from wastewater. Owing to its potent -NH2 functionalization, PTC hydrazidine not only served as an efficient chelator to effectively supply coordinating sites and construct hierarchical porous structures on Pb-PTC-CE, but it also made it possible for cross-linking to occur through the glyoxal cross-linker. The abundant chelators, along with the hierarchical porous construction of the developed Pb-PTC-CE with PTC functionality, result in a greater sorption capacity of 336 mg/g and a short sorption period of 40 min for Pb2+. Additionally, Pb-PTC-CE exhibits highly selective Pb2+ uptake compared to competing ions. This study proposes a feasible methodology for the development of high-quality materials for Pb2+ remediation by combining the advantages of active ligand functionality with ion-imprinting techniques in a straightforward way.

Fabrication and characterization of Araucaria gum/calcium alginate composite beads for batch and column adsorption of lead ions

In this work, we developed five solid adsorbents such as calcium alginate beads (CG), Araucaria gum (AR) extracted from Araucaria heterophylla tree by chemical precipitation procedures, and Araucaria gum/calcium alginate composite beads (CR21, CR12, and CR11) prepared with different calcium alginate: Araucaria gum ratios (2:1, 1:2, and 1:1, respectively). The synthesized solid adsorbents were characterized utilizing TGA, XRD, nitrogen adsorption/desorption analysis, ATR-FTIR, pHPZC, swelling ratio, SEM, and TEM. Through the batch and column adsorption strategies, we evaluated the effect of adsorbent dose, pH, initial Pb (II) concentration, shaking time, bed height, and flow rate. The data of batch technique indicated that CR11 demonstrated a maximum batch adsorption capacity of 149.95 mg/g at 25 °C. Lead ions adsorption was well fitted by pseudo-second order and Elovich according to kinetic studies, in addition to Langmuir and Temkin models based on adsorption isotherm studies onto all the samples. Thermodynamic investigation showed that Pb (II) adsorption process is an endothermic, physical, and spontaneous process. The highest column adsorption capacity (161.1 mg/g) was achieved by CR11 at a bed height of 3 cm, flow rate of 10 mL/min, and initial Pb+2 concentration of 225 mg/L with 68 min as breakthrough time and 180 min as exhaustion time. Yoon-Nelson and Thomas models applied well the breakthrough curves of Pb (II) column adsorption. The maximum column adsorption capacity was decreased by 11.4 % after four column adsorption/desorption processes. Our results revealed that CR11 had an excellent adsorption capacity, fast kinetics, and good selectivity, emphasizing its potential for its applications in water treatment.