Md. Rabiul Awual

Enhanced trace phosphate removal from water by zirconium(IV) loaded fibrous adsorbent

This study was investigated for the trace phosphate removal at high feed flow rate by ligand exchange fibrous adsorbent. The zirconium(IV) loaded bifunctional fibers containing both phosphonate and sulfonate were used as a highly selective ligand exchange adsorbent for trace phosphate removal from water. The precursory fiber of the bifunctional fibers was co-grafted by polymerization of chloromethylstyrene and styrene onto polyethylene coated polypropylene fiber and then bifunctional fibers were prepared by Arbusov reaction followed by phosphorylation and sulfonation. Phosphate adsorption experimental work was carried out in column approach. Phosphate adsorption increased with decreasing the pH of feed solutions. An increase in the feeds flow rate brings a decrease in both breakthrough capacity and total adsorption. The effect of competing anions on phosphate adsorption systems was investigated. The experimental findings reveal that the phosphate adsorption was not affected in the presence of competing anions such as chloride and sulfate despite the enhancement of the breakthrough points and total adsorption. Due to high selectivity to phosphate species, low concentration level of phosphate (0.22 mg/L) was removed at high feed flow rate of 450 h(-1) in space velocity. The adsorbed phosphate on the Zr(IV) loaded fibrous column was quantitatively eluted with 0.1 M NaOH solution and then the column was regenerated by 0.5M H2SO4 for the next adsorption operation. During many adsorption-elution-regeneration cycles, no measurable Zr(IV) was found in the column effluents. Therefore, the Zr(IV) loaded bifunctional fibrous adsorbent is to be an effective means to treat wastewater to prevent eutrophication in the receiving water bodies for long time without any deterioration.

Selective cesium removal from radioactive liquid waste by crown ether immobilized new class conjugate adsorbent.

Conjugate materials can provide chemical functionality, enabling an assembly of the ligand complexation ability to metal ions that are important for applications, such as separation and removal devices. In this study, we developed ligand immobilized conjugate adsorbent for selective cesium (Cs) removal from wastewater. The adsorbent was synthesized by direct immobilization of dibenzo-24-crown-8 ether onto inorganic mesoporous silica. The effective parameters such as solution pH, contact time, initial Cs concentration and ionic strength of Na and K ion concentrations were evaluated and optimized systematically. This adsorbent was exhibited the high surface area-to-volume ratios and uniformly shaped pores in case cavities, and its active sites kept open functionality to taking up Cs. The obtained results revealed that adsorbent had higher selectivity toward Cs even in the presence of a high concentration of Na and K and this is probably due to the Cs-π interaction of the benzene ring. The proposed adsorbent was successfully applied for radioactive Cs removal to be used as the potential candidate in Fukushima nuclear wastewater treatment. The adsorbed Cs was eluted with suitable eluent and simultaneously regenerated into the initial form for the next removal operation after rinsing with water. The adsorbent retained functionality despite several cycles during sorption-elution-regeneration operations.

A weak-base fibrous anion exchanger effective for rapid phosphate removal from water.

This work investigated that weak-base anion exchange fibers named FVA-c and FVA-f were selectively and rapidly taken up phosphate from water. The chemical structure of both FVA-c and FVA-f was the same; i.e., poly(vinylamine) chains grafted onto polyethylene coated polypropylene fibers. Batch study using FVA-c clarified that this preferred phosphate to chloride, nitrate and sulfate in neutral pH region and an equilibrium capacity of FVA-c for phosphate was from 2.45 to 6.87 mmol/g. Column study using FVA-f made it clear that breakthrough capacities of FVA-f were not strongly affected by flow rates from 150 to 2000 h(-1) as well as phosphate feed concentration from 0.072 to 1.6mM. Under these conditions, breakthrough capacities were from 0.84 to 1.43 mmol/g indicating high kinetic performances. Trace concentration of phosphate was also removed from feeds containing 0.021 and 0.035 mM of phosphate at high feed flow rate of 2500 h(-1), breakthrough capacities were 0.676 and 0.741 mmol/g, respectively. The column study also clarified that chloride and sulfate did not strongly interfere with phosphate uptake even in their presence of equimolar and fivefold molar levels. Adsorbed phosphate on FVA-f was quantitatively eluted with 1M HCl acid and regenerated into hydrochloride form simultaneously for next phosphate adsorption operation. Therefore, FVA-f is able to use long time even under rigorous chemical treatment of multiple regeneration/reuse cycles without any noticeable deterioration.

Efficient adsorbents of nanoporous aluminosilicate monoliths for organic dyes from aqueous solution

Growing public awareness on the potential risk to humans of toxic chemicals in the environment has generated demand for new and improved methods for toxicity assessment and removal, rational means for health risk estimation. With the aim of controlling nanoscale adsorbents for functionality in molecular sieving of organic pollutants, we fabricated cubic Im3m mesocages with uniform entrance and large cavity pores of aluminosilicates as highly promising candidates for the colorimetric monitoring of organic dyes in an aqueous solution. However, a feasible control over engineering of three-dimensional (3D) mesopore cage structures with uniform entrance (~5 nm) and large cavity (~10 nm) allowed the development of nanoadsorbent membranes as a powerful tool for large-quantity and high-speed (in minutes) adsorption/removal of bulk molecules such as organic dyes. Incorporation of high aluminum contents (Si/Al=1) into 3D cubic Im3m cage mesoporous silica monoliths resulted in small, easy-to-use optical adsorbent strips. In such adsorption systems, natural surfaces of active acid sites of aluminosilicate strips strongly induced both physical adsorption of chemically responsive dyes and intraparticle diffusion into cubic Im3m mesocage monoliths. Results likewise indicated that although aluminosilicate strips with low Si/Al ratios exhibit distortion in pore ordering and decrease in surface area and pore volume, enhancement of both molecular converges and intraparticle diffusion onto the network surfaces and into the pore architectures of adsorbent membranes was achieved. Moreover, 3D mesopore cage adsorbents are reversible, offering potential for multiple adsorption assays.

Rapid column-mode removal of arsenate from water by crosslinked poly(allylamine) resin.

Performances of crosslinked poly(allylamine) resin (PAA) as arsenate (As(V)) adsorbent were studied using a column packed with PAA in hydrochloride form. PAA has a high amino group content of 14.6 mmol/g in free amine form and a high chloride content of 10.2 mmol/g in hydrochloride form. Its wet volumes in water were 4.5 and 3.1 mL/g in hydrochloride and free amine forms, respectively, indicating its high hydrophilicity. Breakthrough capacities for As(V) were evaluated changing conditions of adsorption operations: pH of feeds from 2.2 to 7.0, concentration of As(V) in feeds from 0.020 to 2.0 mM, and feed flow rate from 250 to 4000 h(-1) in space velocity. Breakthrough capacities increased from 2.6 to 3.4 mmol/g with a decrease in pH from 7.0 and 2.2, and also from 0.81 to 2.8 mmol/g with an increase in As(V) concentration from 0.020 to 2.0mM. When feed flow rate increased from 250 to 4000 h(-1), breakthrough capacities changed form 3.5 to 0.81 mmol/g. Because of non-Hofmeister anion selectivity behavior of PAA, the interference of chloride and nitrate was minor. Although PAA slightly preferred As(V) to sulfate, the latter more markedly interfered with uptake of As(V) than chloride and nitrate. Competitive uptake of As(V) and phosphate revealed that PAA slightly preferred phosphate to As(V). The adsorbed As(V) was quantitatively eluted with 2M HCl and PAA was simultaneously regenerated into hydrochloride form. All results were obtained using the same column without change of the packed PAA and any deterioration in column performances for 4 months.

Selective lanthanide sorption and mechanism using novel hybrid Lewis base (N-methyl-N-phenyl-1,10-phenanthroline-2-carboxamide) ligand modified adsorbent

This study aims to develop a highly selective Lewis base adsorbent to investigate the selective sorption and recovery of Eu(III) and Sm(III) from wastewater. The oxygen and nitrogen donor atoms containing Lewis base N-methyl-N-phenyl-1,10-phenanthroline-2-carboxamide (MePhPTA) ligand was synthesized and subsequently an adsorbent was prepared by direct immobilization onto mesoporous silica. Determined maximum adsorption capacities were 125.63 and 124.38 mg/g for Eu(III) and Sm(III), respectively. Experiments with mixed-cations solutions showed that the sequence of preferential adsorption was Eu(III)>Sm(III). The lanthanide sorption by hybrid Lewis base adsorbent (HyLBA) was not adversely affected by the presence of sodium, potassium, calcium, magnesium, chloride, sulfate and nitrate ions due to strong affinity between hard Lewis acid lanthanide and hard Lewis base adsorbent. The crystallography for the Sm-MePhPTA complex suggested that MePhPTA was strongly coordinated to Sm(III) with oxygen and nitrogen by forming a stable complex with two 5-membered rings. The data clarified that bond lengths between Sm(III) and amide oxygen (2.475Å) were shorter than SmN (2.662Å) in phenanthroline moiety indicating strong oxygen driven HyLBA. The results suggested that HyLBA has a good prospect of promising applications for separation/sorption of lanthanide ions from effluents.

Removal of trace arsenic(V) and phosphate from water by a highly selective ligand exchange adsorbent

A highly selective ligand exchange type adsorbent was developed for the removal of trace arsenic(V) (As(V)) and phosphate from water. This adsorbent was prepared by loading zirconium(IV) on monophosphonic acid resin. This adsorbent was able to remove toxic anions efficiently at wide pH ranges. However, low pH was preferable for maximum breakthrough capacity in an adsorption operation. The effect of a large amount of competing anions such as chloride, bicarbonate, and sulfate on the adsorption systems of As(V) and phosphate anions was investigated. The experimental findings revealed that the As(V) and phosphate uptakes were not affected by these competing anions despite the enhancement of the breakthrough points and total adsorption. Phosphate anion was slightly preferable than As(V) in their competitive adsorption by the adsorbent. The adsorbed As(V) and phosphate on the Zr(IV)-loaded resin were quantitatively eluted with 0.1 mol/L sodium hydroxide solution, and the adsorbent was regenerated by 0.5 mol/L sulfuric acid. During several cycles of adsorption-elution-regeneration operations, no Zr(IV) was detected in the column effluents. Therefore, the Zr(IV)-loaded monophosphonic acid resin is an effective ligand exchange adsorbent for removing trace concentrations of As(V) and phosphate from water.

Large three-dimensional mesocage pores tailoring silica nanotubes as membrane filters: nanofiltration and permeation flux of proteins

Large three-dimensional (3D) mesocage structures that have multidirectional pore networks and uniform openings perpendicular to the longitudinal axis of NTs are of particular interest in terms of their potential. This paper reports on the feasibility of direct control of 3D mesopore cage structures throughout silica nanotubes (NTs) vertically aligned inside Anodic Alumina Membrane (AAM) nanochannels without the use of any organic stabilizing modifiers. This is the first reported study which uses direct synthesis of ordered cubic Im3m mesocage structures inside well-aligned silica-NTs that have open surfaces of top-bottom ends, and multidirectional (3D) mesopore connectivity. These 3D mesocage silica-NT arrays hybrid AAM channels function as nanofilters that can rapidly (in seconds) separate large quantities of proteins. In this nanofiltration assay, three proteins that differ in molecular weight and size such as cytochrome c (CytC), myoglobin (Mb), and hemoglobin (Hb) were used. The prominent factors affecting nanofiltration and permeation flux performance of nanoscale cage membranes are: (i) the concentration of the feed solution of protein (retentate), (ii) molecular sizes and weights of proteins, and (iii) stability of the hierarchical mesocage structures during the filtration and permeation processes. Although the protein nanofiltration efficiency decreased during the reuse cycles of the nanofilter membranes, the proposed nanofilters still exhibited well-controlled molecular-size cut-off after a number of cycles. These mesocage silica-NT-supported membranes are expected to be promising for the development of new generation high-precision, uniform-porosity, and bio-compatible nanofilters with molecular-size cut-off systems.

Optical mesosensors for monitoring and removal of ultra-trace concentration of Zn(II) and Cu(II) ions from water

Optical captor design is necessary for the controlled development of a technique for detecting and removing heavy and toxic metals from drinking water with high flexibility and low capital cost. We designed chemical mesocaptors for optical separation/extraction and monitoring/detection of Cu(II) and Zn(II) ions from water even at trace concentration levels without a preconcentration process. The mesoporous aluminosilica carriers with three-dimensional (3D) structures, high aluminum content, natural surfaces, and active acid sites strongly induced H-bonding and dispersive interactions with organic moieties, thereby leading to the formation of stable captors without chromophore leaching during the removal assays of Cu(II) and Zn(II) ions. Using such a tailored mesocaptor design, the direct immobilization of these hydrophobic ligands (4,5-diamino-6-hydroxy-2-mercaptopyrimidine and diphenylthiocarbazone) into ordered pore-based aluminasilica monoliths enabled the easy generation and transduction of optical colour signals as a response to metal-to-ligand binding events, even at ultra-trace concentrations (~10(-9) mol dm(-3)) of Cu(II) and Zn(II) ions in drinking water, without the need for sophisticated instruments. Theoretical models have been developed to provide insights into the effect of active site surfaces on the enhancement of the optical removal process in terms of long-term stability, reversibility, and selectivity, hence allowing us to understand the role of mesoscopic geometry and nanoscale pore orientation of mesocaptors better. Generally, this ion-capture model enables the development of a simple and effective technique for effective wastewater treatment and management.

A Reliable Hybrid Adsorbent for Efficient Radioactive Cesium Accumulation from Contaminated Wastewater.

Cesium (Cs) removal from nuclear liquid wastewater has become an emerging issue for safeguarding public health after the accident at the Fukushima Daiichi Nuclear Power Plant. A novel macrocyclic ligand of o-benzo-p-xylyl-22-crown-6-ether (OBPX22C6) was developed and successfully immobilized onto mesoporous silica for the preparation of hybrid adsorbent. The benzene ring π electron is the part of crown ether of OBPX22C6 for easy orientation of the macrocyclic compound for making the π electron donation with Cs complexation. The potential and feasibility of the hybrid adsorbent as being Cs selective was evaluated in terms of sensitivity, selectivity and reusability. The results clarified that the Cs removal process was rapid and reached saturation within a short time. Considering the effect of competitive ions, sodium (Na) did not markedly affect the Cs adsorption whereas potassium (K) was slightly affected due to the similar ionic radii. However, the oxygen in long ethylene glycol chain in OBPX22C6 was expected to show strong coordination, including Cs-π interaction with Cs even in the presence of the high amount of K and Na. Due to its high selectivity and reusability, significant volume reduction is expected as this promising hybrid adsorbent is used for Cs removal in Fukushima wastewater.