Bincheng Xu

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.

Optimized preparation of micro-block CPAM by response surface methodology and evaluation of dewatering performance

Micro-block cationic polyacrylamide (P(AM-MAPTAC)) was synthesized through UV-initiated template copolymerization and characterized by FTIR, 1H NMR, SEM and TG/DSC analyses. Furthermore, the main influence factors of the preparation process were optimized through Box–Behnken experiment design and Respond Surface Method (RSM). The maximum intrinsic viscosity of micro-block CPAM was 13.223 dL g−1 under the optimum synthesis conditions. The dewatering performance of micro-block CPAM was evaluated taking activated sludge collected from a dyeing mill as the processing object. Results showed that the micro-block CPAM exhibited excellent dewatering performance. At a 30 mg L−1 dosage of micro-block CPAM, the residual turbidity, filter cake moisture content, specific resistance to filtration and chemical oxygen demand removal rate reached 4.47 NTU, 72.2%, 5.47 (1012 m kg−1) and 79.2%, respectively. Dewatering tests not only demonstrated the superiority of micro-block P(AM-MAPTAC) synthesized by UV-initiated template copolymerization over that synthesized by traditional methods but also demonstrated that increasing the molecular weight can further enhance the dewatering performance of flocculants.

Formation of cationic hydrophobic micro-blocks in P(AM-DMC) by template assembly: characterization and application in sludge dewatering

A template assembly method was introduced to obtain a cationic hydrophobic micro-block structure based amphiphilic electrolyte poly(acrylamide-co-2-methacryloxyethyltrimethyl ammonium chloride) P(AM-DMC) in this work, thereby increasing charge density and enhancing charge neutralization ability at the same charge density. The alteration of copolymerization or homo-polymerization was evaluated by the changes in reactivity ratios, so as to unravel the mechanism of template assembly. The micro-blocks generated by the new distribution of sequences were demonstrated by 1H nuclear magnetic resonance spectroscopy (1H NMR) and differential thermal-thermogravimetric analysis (DSC-TGA). Two negative controls were employed in sludge dewatering experiments to further evaluate the advanced properties of the template-assembled polymer. The results further verified that the positive effect of template assembly on flocculation performance of the polymer was achieved mainly through two ways: improving charge density and generating the micro-block structure. It can be concluded that the introduction of template assembly into polymerization can improve the performance of the polymer.

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.

Poly(2-acrylamido-2-methylpropane sulfonic acid) grafted magnetic chitosan microspheres: Preparation, characterization and dye adsorption

A novel chitosan-based magnetic adsorbent [poly(2-acrylamido-2-methylpropane sulfonic acid) grafted magnetic chitosan microspheres, PMCMs] was successfully fabricated via free radical polymerization for effectively removing the cationic dye methylene blue (MB). The effects of initial solution pH (1.0-10.0), temperature (30-50°C), contact time (0-660min) and initial concentration (50-1600mg/L) were studied. The results indicated that the adsorption capacity increased with the increasing of initial solution pH and temperature. The adsorption kinetic and adsorption equilibrium data fitted closely to the pseudo-second-order kinetic model and Langmuir isotherm model respectively, confirming monolayer adsorption. The maximum adsorption capacity of PMCMs for MB at initial solution 9.0 were 1000, 1250 and 1428mg/g at 30, 40 and 50°C, respectively. Furthermore, the magnetic microspheres could be easily separated using a magnet and effectively regenerated after finishing the treatment process. Therefore, PMCMs are promising candidates for the removal of dye from wastewater.

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.

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.