Shixin Zhang

Ultrasound-initiated synthesis of cationic polyacrylamide for oily wastewater treatment: Enhanced interaction between the flocculant and contaminants

Weak interaction between flocculants and oil is a main bottleneck in the treatment of oil-containing wastewater. To solve this problem, a novel flocculant PAB with cationic micro-block structure and hydrophobic groups of benzene rings was synthesized by ultrasound initiated polymerization technique and applied to remove turbidity and oil from water. To avoid unnecessary addition of reagents in traditional template and micellar copolymerization, surface-active monomer benzyl(methacryloyloxyethyl)dimethylammonium chloride (BMDAC) with self-assembly ability in aqueous solution was employed to synthesize flocculants. The critical association concentration of BMDAC measured by conductivity and surface tension methods was 0.014 mol·L-1. The results of reactivity ratio, statistical analysis of sequence-length distribution and 1H NMR provided evidence for the synthesis of copolymer with cationic micro-block. In addition, the apparent viscosity measurement indicated that PAB had an obvious hydrophobic association property. Finally, flocculation tests demonstrated that flocculation performance was greatly improved by adding PAB and the removal rate of oil and turbidity both reached the maximum (87.5% and 92%) at dosage of 40 mg·L-1 and pH of 7.0. Flocculation mechanism investigation demonstrated that the cooperation of charge neutralization, adsorption bridging, and hydrophobic association effect played an important role. The formed flocs by PAB was large, compact, difficult to break, and easy to regrow because of the enhanced interaction between flocculants and oil. In summary, this study can provide important reference in the design of organic flocculants in oily wastewater treatment applications.

Rapid and efficient removal of heavy metal and cationic dye by carboxylate-rich magnetic chitosan flocculants: Role of ionic groups

A multifunctional carboxylate-rich magnetic chitosan flocculant (Mag@PIA-g-CS) was prepared through surface graft copolymerization on magnetite particles. The effect of monomer molar ratio, initiator and pre-neutralized degree on polymerization rate was determined. Various analytical methods were applied to characterize Mag@PIA-g-CS, exhibiting the successful grafting of polymers, good magnetic feature and core-shell structure. The kinetic process of Ni(II) and malachite green (MG) flocculation by Mag@PIA-g-CS reached equilibrium within <60min with the optimal uptake rate of 98.3% and 87.4%, and exhibited satisfactory removal effect in wide pH range (4.0-8.0 for Ni(II), 5.0-10.0 for MG). Mag@PIA-g-CS exhibited superior flocculation performance over chitosan magnetic flocculant (Mag@CS). The pH-dependent behavior, rapid responsiveness and sensitivity to ionic strength in batch flocculation tests indicated the distinct effect of ionic groups. Moreover, sweeping action of linear molecular chains facilitated further flocculation. Mag@PIA-g-CS showed high stability in extreme environments, and can be easily regenerated and separated.

Enhancement of textile-dyeing sludge dewaterability using a novel cationic polyacrylamide: role of cationic block structures

In this study, a novel cationic polyacrylamide (CPAM) with a microblock structure was successfully synthesized through ultrasonic-initiated template copolymerization (UTP) using allyltrimethylammonium chloride (TM) and acrylamide (AM) as monomers, and sodium polyacrylate (NaPAA) as a template. Fourier transform infrared spectroscopy (FT-IR), 1H (13C) nuclear magnetic resonance spectroscopy (1H (13C) NMR), and thermogravimetric analysis (TGA) were employed to characterize the properties of the polymers. The results showed that the novel cationic microblock structure was formed in the template copolymer of TM and AM (TPTA). Besides, the copolymerization was demonstrated to follow an I zip-up (ZIP) template polymerization mechanism through the analysis of association constant (MK) and polymerization kinetics. The flocculation results of textile-dyeing sludge dewatering revealed that the polymer with the novel microblock structure showed an excellent flocculation performance. When the optimal conditions at pH of 7.0, dosage of 40 mg L−1 and the intrinsic viscosity of 2.3 dL g−1, the minimum SRF of 4.9 × 1012 m kg−1 and FCMC of 72.1% were observed. During the flocculation process, the cationic microblocks in TPTA extremely enhanced the ability of charge neutralization and bridging, and contributed much to the excellent flocculation performance in textile-dyeing sludge dewatering.

Effect of the Cationic Block Structure on the Characteristics of Sludge Flocs Formed by Charge Neutralization and Patching

In this study, a template copolymer (TPAA) of (3-Acrylamidopropyl) trimethylammonium chloride (AATPAC) and acrylamide (AM) was successfully synthesized though ultrasonic-initiated template copolymerization (UTP), using sodium polyacrylate (PAAS) as a template. TPAA was characterized by an evident cationic microblock structure which was observed through the analyses of the reactivity ratio, Fourier transform infrared spectroscopy (FTIR), 1H (13C) nuclear magnetic resonance spectroscopy (1H (13C) NMR), and thermogravimetry/differential scanning calorimetry (TG/DSC). The introduction of the template could improve the monomer (AATPAC) reactivity ratio and increase the length and amount of AATPAC segments. This novel cationic microblock structure extremely enhanced the ability of charge neutralization, patching, and bridging, thus improving the activated sludge flocculation performance. The experiments of floc formation, breakage, and regrowth revealed that the cationic microblock structure in the copolymer resulted in large and compact flocs, and these flocs had a rapid regrowth when broken. Finally, the larger and more compact flocs contributed to the formation of more channels and voids, and therefore the specific resistance to filtration (SRF) reached a minimum.

Ultrasonic-template technology inducing and regulating cationic microblocks in CPAM: characterization, mechanism and sludge flocculation performance

In this study, the ultrasonic-template polymerization technique (UTPT) was used to generate and regulate the distribution of cationic microblocks in a polymer. The ultrasonic-template copolymer (TPAD-U) of acrylamide (AM) and methacryloxyethyl trimethyl ammonium chloride (DMC) with a novel cationic microblock structure was successfully synthesized through UTPT using sodium polymethacrylate (PMAA) as the template. Fourier transform infrared spectroscopy (FT-IR), 1H (13C) nuclear magnetic resonance spectroscopy (1H (13C) NMR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were employed to characterize the properties of the polymers. The results showed that evident cationic microblocks formed in TPAD-U. Moreover, the template polymerization mechanism and reaction kinetics were analyzed, and the results showed that the I (ZIP) mechanism and free radical termination were assigned to template copolymerization. The I (ZIP) template mechanism convincingly indicated the formation of the cationic microblocks. The sludge dewatering results demonstrated that TPAD-U showed a better sludge flocculation performance than flocculants prepared by the non-template polymerization technique. During the sludge flocculation process, the cationic microblocks in TPAD-U greatly enhanced the effects of charge neutralization and bridging, which contributed much to a prominent flocculation performance.

Fabricating an anionic polyacrylamide (APAM) with an anionic block structure for high turbidity water separation and purification

Ultraviolet (UV)-initiated template polymerization (UTP) was used as a feasible strategy to prepare a novel anionic polyacrylamide (APAM) with a microblock structure. In the template copolymerization system, acrylamide (AM) and sodium allylsulfonate (SAS) were used as monomers, and poly (allylammonium chloride) (PAAC) as a template. The chemical properties of the polymers were observed by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), 1H (13C) nuclear magnetic resonance spectroscopy (1H (13C)), and thermogravimetry/differential scanning calorimetry (TG/DSC). Results showed that the novel anionic microblock structure was formed in the template copolymer. Besides, the results of the association constant (KM) indicated that the copolymerization followed I Zip-up (ZIP) template polymerization mechanism, which indicated the formation of the microblock structure again. Parameters such as pH and dosage that affected the flocculation performance, flocculation kinetics and the FTIR spectra of the generated flocs were investigated to further observe the effect of anionic microblocks on flocculation performance and understand the relationship between the flocs and flocculants. Flocculation experimental results demonstrated that the anionic microblocks in the template copolymer could enhance the charge neutralization and bridging ability, and therefore an excellent flocculation performance of treating high turbidity water was observed.

Using ultrasonic (US)-initiated template copolymerization for preparation of an enhanced cationic polyacrylamide (CPAM) and its application in sludge dewatering

In this study, the ultrasonic (US)-initiated template copolymerization was employed to synthesize a novel cationic polyacrylamide (CPAM) characterized by a microblock structure using dimethyldiallylammonium chloride (DMDAAC) and acrylamide (AM) as monomers, and sodium polyacrylate (NaPAA) as template. The polymers structure property was analyzed by Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance spectroscopy (1H NMR) and thermogravimetric analysis (TGA). The results showed that a novel cationic microblock structure was successfully synthesized in the template copolymer of DMDAAC and AM (TPADM). Meanwhile, the analysis result of association constant (MK) provided powerful support for a I Zip-up (ZIP) template polymerization mechanism and the formation of the microblock structure. The factors affecting the polymerization were investigated, including ultrasonic power, ultrasonic time, monomer concentration, initiator concentration, mAM:mDMDAAC and nNaPAA:nDMDAAC. The sludge dewatering performance of the polymers was evaluated in terms of specific resistance to filtration (SRF), filter cake moisture content (FCMC), floc size (d50) and fractal dimension (Df). Flocculation mechanism was also analyzed and discussed. The sludge dewatering results revealed that the polymer with the novel microblock structure showed a more excellent flocculation performance than those with randomly distributed cationic units. A desirable flocculation performance with a SRF of 4.5 × 1012 m kg-1, FCMC of 73.1%, d50 of 439.156 µm and Df of 1.490 were obtained at pH of 7.0, dosage of 40 mg L-1 and the molecular weight of 5.0 × 106 Da. The cationic microblock extremely enhanced the polymer charge neutralization and bridging ability, thus obtaining the excellent sludge dewatering performance.

Polymer-grafted magnetic microspheres for enhanced removal of methylene blue from aqueous solutions

Novel polymer-grafted magnetic microspheres (GMMs) were prepared by graft polymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and acrylic acid (AA) onto the surface of chitosan/magnetite composite microspheres (MMs). The magnetic microspheres were fully characterized and then applied to the adsorption of a cationic dye (methylene blue, MB) from aqueous solutions. Results show that the adsorption capacity of GMMs was notably enhanced compared with MMs. Furthermore, the effects of initial solution pH, contact time and initial concentration on MB adsorption by GMMs were systematically investigated. The adsorption kinetics and adsorption isotherms are well described by pseudo-second-order kinetic model and Langmuir isotherm model respectively, suggesting the adsorption is a homogeneous monolayer adsorption. The maximum MB adsorption capacity by GMMs is found to be 925.9 mg g−1 at 298.15 K and initial solution pH 9.0, as determined from the Langmuir isotherm. The MB-loaded GMMs can be rapidly separated and effectively regenerated at pH 2.0.

Evaluation of a novel dextran-based flocculant on treatment of dye wastewater: Effect of kaolin particles

Graft modified flocculants have recently received increasing attention in the field of water treatment as they have the combinative advantages of synthetic and natural polymeric flocculants. In this work, surface-active monomer benzyl(methacryloyloxyethyl)dimethylammonium chloride (BMDAC) was selected to graft on dextran (DX) with high molecular weight (10.3 × 106 g/mol) produced through enzyme-catalyzed process in order to remove dissolved dyes from wastewater. The flocculant (DAB) was fabricated by ultrasound initiated polymerization technique, and the structure characterization of FTIR, 1H/12C NMR, XRD and XPS spectrum confirmed the successful grafting. Then the Congo red (CR) removal efficiency by DAB was optimized based on the flocculation conditions, including wastewater initial pH, flocculant dosage and initial dye concentration. The effect of suspended solids on the removal of dyes was evaluated in kaolin-CR simulated wastewater. The results indicated that the optimal removal efficiency of CR was 68.1% and 88.2% in single CR and kaolin-CR flocculation system, respectively. The improvement of removal efficiency was attributed to the fact that partial CR molecules were adsorbed onto kaolin particles before flocculation, and were synergistically flocculated accompanied by kaolin particles. Finally, the flocculation mechanism was discussed by a detailed investigation of the zeta potentials, FTIR and XPS spectra of flocs, which can provide important reference for optimizing the flocculation conditions and designing novel high-performance flocculants.

Polymer-Functionalized Magnetic Nanoparticles: Synthesis, Characterization, and Methylene Blue Adsorption

The removal of methylene blue (MB) from wastewater has attracted global concerns. In this study, polymer-functionalized magnetic nanoparticles for MB removal, Fe3O4@SiO2-MPS-g-AA-AMPS (FSMAA), were successfully synthesized by grafting acrylic acid (AA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) on the surface of vinyl-modified Fe3O4@SiO2. With various characterization techniques, it was confirmed that the obtained FSMAA had a core–shell structure, a good magnetic property, and plenty of functional groups on its surface. MB adsorption experiments showed that the adsorption capacity of FSMAA was notably enhanced as the grafted monomer concentration and solution pH were increased. The adsorption kinetic data and isothermal data were well described by the pseudo-second-order kinetic model and the Langmuir model, respectively. The maximum adsorption capacity of FSMAA was 421.9 mg g−1 with grafted monomer concentration at 2.0 mol L−1 and solution pH at 9, much higher than those of other adsorbents stated in previous literatures. Based on XPS analysis, surface adsorption mechanism between FSMAA and MB was electrostatic interaction, hydrogen bonding, and hydrophobic interaction. Furthermore, FSMAA was effectively regenerated by acid pickling, and the remaining adsorption capacity was more than 60% after eight adsorption–regeneration cycles. All the results demonstrated the self-made FSMAA was a desirable adsorbent to remove MB from wastewater.