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Cationic polyacrylamide (CPAM) has been the focus of research in environmental engineering field, particularly in sludge dewatering. However, poor stability of the existing cationic polyacrylamide has limited its application. In the face of the current complex sewage/sludge environment, CPAM with high efficiency, good stability and economy is remarkably desired in this field. In this study, a CPAM (PAMA) with high acid and alkali resistance was synthesized through copolymerization of acrylamide (AM) and methacrylamido propyl trimethyl ammonium chloride (MAPTAC) under ultraviolet (UV) radiation. The structure, morphology as well as the thermal decomposition property were analyzed through instrumental analysis. Furthermore, influencing factors of the copolymerization reaction were investigated and discussed in detail. The dewatering performance of PAMA was also evaluated by measuring the supernatant residual turbidity (RT), moisture content of the filter cake (FCMC), and specific resistance to filtration of the sludge (SRF). The RT, FCMC, and SRF reached 4.70 NTU, 71%, and 3.94 (10 12 m Kg −1 ), respectively, at 40 mg L −1 of PAMA-25-15.1 and pH of 6.0. Furthermore, these indices did not increase with the pH changes of the original sludge, and which indicated a high acid and alkali resistance of PAMA. [ABSTRACT FROM AUTHOR]

• The β-cyclodextrin grafted flocculants were synthesized by ultrasound-assisted method. • The synthesized conditions of CADs were optimized. • CADs showed excellent flocculation performance in treating HA-kaolin wastewater. • The interaction effect between β-CD and HA could improve flocculation performance. In this work, the novel β-cyclodextrin based polymeric flocculants (CADs) were synthesized and applied on the treatment of humic acid (HA)-kaolin wastewater. Acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (DAC) were grafted onto β-cyclodextrin (β-CD) by ultrasound assisted initiation using ceric ammonium nitrate as initiator. The synthesized conditions were optimized by evaluating the intrinsic viscosity and grafting efficiency of CADs. Furthermore, the characterization methods including Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance spectroscopy (1H NMR), thermogravimetric/differential scanning calorimetry (TG/DSC) and scanning electron microscopy (SEM) were used to evaluate and analyze the molecular structure and surface morphology of graft copolymers. In flocculation experiments, the effects of dosage, flocculant types, solution pH and flocs properties on flocculation performance were investigate in detail. CADs exhibited more satisfactory turbidity and HA removal performance than the synthetic cationic flocculants (PAD) and the non-ionic graft polymers (CAM). At the optimum dosage 4 mg/L, the maximum turbidity and HA removal rate of CAD 1# was 97.5% and 68.3%, respectively. Furthermore, CAD 1# exhibited a good flocculation performance and wide flocculation window in the pH range of 2.0–8.0. Lastly, the flocculation mechanism of CAD was detailed discussed by the investigation of zeta potential, surface tension, flocs FTIR and XPS spectra. Results indicated the unique hydrophobic internal structure of β-CD played an important role in improving the removal rate HA of CAD. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Chitosan-based flocculants with chelation and flocculation capacity are designed and prepared. • Relationship between flocculants structural and chelation-flocculation is investigated. • There is a certain linear relationship between heavy metal concentration and flocculants dosage. • Copper ions in mixed heavy metals solutions is preferentially chelated and flocculated. • The work provided valuable guidance in the design of eco-friendly polymeric flocculants. Abstract Dual-function chitosan-based flocculants with chelation and flocculation capacity, carboxylated chitosan-graft-polyacrylamide (PCA), carboxylated chitosan-graft-polyacrylamide-co-sodium xanthate (PCAXC), and carboxylated chitosan-graft-poly(acrylamide-2-acrylamido-2-methylpropane sulfonic acid) (PCAAF), are designed and prepared by UV initiation method. The physicochemical characteristics of PCA, PCAXC, and PCAAF were characterized by fourier transform infrared spectroscopy, 1H nuclear magnetic resonance, and X-ray diffraction pattern to confirm the successful syntheses. Then PCA, PCAXC, and PCAAF are applied to chelate and flocculate Cu, Cr, and Ni from water. Effects of pH, flocculants dosage, reaction time, and stirring speed were investigated systematically to detect the relationship between flocculants structural and chelation-flocculation capacity. The maximum removal rate of Cu and Cr obtained by PCAXC at are 85.1% and 76.1%, respectively, while The maximum removal rate of Ni obtained by PCAAF at is more than 75.7%%. In addition, the relationship between the initial concentration of simulated heavy metal wastewater and the flocculants dosage and the competitive chelation-flocculation properties in the mixed heavy metal solution are also detected in detail. The mechanism can be assigned to the effective interaction between function groups of the flocculants and heavy metal irons by chelation, charge neutralization, and adsorption bridging mechanism. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A functionalized chitosan-based flocculant (MHCS-g-P(AM-DAC)) is synthesized by UV initiation. • The concentration of algae decreased as the flocculants dosage increased. • The removal efficiency of MHCS-g-P(AM-DAC) was higher than that of commercially available coagulant. • MHCS-g-P(AM-DAC) has high efficiency in the removal of algae and turbidity from raw water. Abstract The graft copolymer flocculant of chitosan namely, maleoyl chitosan-graft-poly(acrylamide–acryloxyethyl trimethyl ammonium chloride) [MHCS-g-P(AM-DAC)], was prepared by UV initiation to improve the solubility and flocculation efficiency of chitosan. Flocculating properties for algae removal were studied systematically. The effects of parameters such as monomer concentration, MHCS content, illumination time, photoinitiator concentration, cationic degree, pH and grafting efficiency over synthesis process of MHCS-g-P(AM-DAC) were studied. The characterization of obtained MHCS-g-P(AM-DAC) were carried out through different analytic techniques. The influences of dosage, pH, and G value on the flocculating properties were also investigated to support that MHCS-g-P(AM-DAC) was more effective than organic flocculant (CPAM) and inorganic coagulant (PFS and PAC) on algae removal. The flocculation mechanisms of MHCS-g-P(AM-DAC) were determinate by obtained zeta values. [ABSTRACT FROM AUTHOR]

[Display omitted] • P(DAC-NIPAM) significantly improved the removal of levofloxacin and tetracycline. • P(DAC-NIPAM) had strong interaction with antibiotics for its multiple functional groups. • The hydrophobic groups on P(DAC-NIPAM) tightly bridged micelles of antibiotics and SDS. • Compact flocs were formed for shrinkage of P(DAC-NIPAM) molecule at the LCST. • Flocculation simulation further confirmed application feasibility of thermosensitive flocculants. Antibiotics were detected in worldwide natural water especially in COVID-19 period. The common flocculants rarely removed the dissolved antibiotics from natural water and wastewater. The flocculation improvement of organic polymer flocculants might solve the issue of antibiotic pollution or promote the removal efficiencies of antibiotics in water/wastewater treatment plants. Herein, a thermosensitive flocculant, P(DAC-NIPAM), was prepared via one-step method. It was investigated that the relationship between the various functional groups of P(DAC-NIPAM) and its flocculation performances in the treatment of simulated water containing levofloxacin, tetracycline, colloidal particles and natural organic matters. The removal mechanisms were discussed. The results indicated that the rich cationic, hydrophilic and hydrophobic groups of P(DAC-NIPAM) enhanced the interaction between flocculants and pollutants. The bridging of P(DAC-NIPAM) among micelles, charge neutralization, hydrogen bond between P(DAC-NIPAM) and two antibiotics, the shrinkage of P(DAC-NIPAM) molecule and enhancement of hydrophobicity when water temperature was above low critical solution temperature (LCST), co-flocculation and co-settlement of multiple pollutants all contributed to the efficient removal of levofloxacin and tetracycline from water. Flocculation simulation further confirmed that thermosensitive flocculant combined with heating plates was a potential candidate for antibiotic treatment in actual water treatment plants. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amphoteric starch-based flocculants were synthesized by low-pressure UV initiation. • Amphoteric starch-based flocculants show high flocculation performance. • Amphoteric starch-based flocculants exhibit low salts sensitivity. • Flocculation mechanism includes charge neutralization, patching and bridging. Surface charges of the suspended colloidal particles in real water can be either negative or positive. Flocculation is one of the most widely used technologies in water treatment. A series of amphoteric starch-based flocculants (denoted as ASBFs) with the same chemically modified functional groups but different charge degrees and intrinsic viscosities were successfully via low-pressure ultraviolet initiation and used for the removal of different charged contaminants from water. The characterization results confirmed the successful grafting acrylamide (AM) and 2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) onto carboxymethyl starch. Different influencing factors, including flocculant dosage, contaminants concentration, pH of solution, stirring speed, sedimentation time and various salts, were investigated systematically. ASBFs with eco-friendliness exhibited high flocculation property, low optimal dosage and low salts sensitivity, for not only kaolin, but also hematite suspensions. The zeta potential (ZP) measurement suggested that the removal mechanism mainly includes charge neutralization, patching and bridging. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high-efficiency, multifunctional, salt/pH-tolerant magnetic flocculant was successfully prepared. • The growth characteristics of flocs are systematically elucidated. • There is a positive correlation between the fractal dimension of flocs and flocculation efficiency. • Ca(II) and Fe(III) will promote the removal of DB56 and Cu(II), respectively. • The neural network models can accurately predict the removal rate of DB56 and Cu(II). In this study, an amphoteric magnetic chitosan (CS)-based flocculant MFe 3 O 4 @CS-g-PIA was prepared from CS, Fe 3 O 4 , and itaconic acid (IA), and its apparent morphology and characteristic structure were systematically studied. The flocculation performance and mechanism of the fabricated material were also investigated in different pollution systems, and the effects of total monomer concentration, m(CS):m(IA), IA pre-neutralization degree, reaction temperature, reaction time, and initiator concentration on the synthesis of MFe 3 O 4 @CS-g-PIA were studied. Characterization results showed that MFe 3 O 4 @CS-g-PIA forms a three-dimensional network with excellent magnetic induction. The optimal removal rates of Cu(II) and Disperse Blue 56 (DB56; 90.2% and 97.0%, respectively) were obtained under the conditions of 150 mg·L−1 MFe 3 O 4 @CS-g-PIA, pH 6.0, and 300 rpm stirring speed. MFe 3 O 4 @CS-g-PIA maintained removal rates of over 80.0% for Cu(II) and DB56 after five consecutive cycles of regeneration/flocculation and demonstrated excellent acid resistance stability. Changes in the particle size distribution, fractal dimensions, and zeta potentials of the flocs indicated that the relevant flocculation mechanism involves the synergistic functions of chelation, charge neutralization, and adsorption bridging. An artificial neural network model was finally established on the basis of the experimental flocculation data to predict the removal rates of Cu(II) (R = 0.97) and DB56 (R = 0.98) accurately. [ABSTRACT FROM AUTHOR]

[Display omitted] • The copolymerization reaction was separately initiated by photocatalyst and photoinitiator. • The initiation and synthesis mechanisms of CS-g-DAC (T) and CS-g-DAC (V) were different. • CS-g-DAC (V) prepared by V A-044 owned the little higher initiation efficiency than CS-g-DAC (T). • The ratio of C-N to C = N in the molecular structure of CS-g-DAC (T) was lower. • CS-g-DAC (T) possessed the little more outstanding performances in water treatment. Flocculants as the traditional water treatment agents were widely applied in water treatment, sludge thickening and dewatering, oil exploitation and papermaking. The synthesis of organic polymer flocculants via high-efficient initiation system has aroused special attention in the development of flocculant. Herein, a chitosan-based flocculant (CS-g-DAC (T)) was synthesized through ultraviolet (UV) initiation of titanium dioxide (TiO 2) It was compared with other chitosan-based flocculant (CS-g-DAC (V)) synthesized by a traditional photoinitiator, V A-044 , in terms of initiation efficiency, initiation mechanism, flocculant characteristics, molecular structures and flocculant performances in water treatment. Holes (h+), superoxide radicals (O 2 •-) and hydroxyl radicals (OH) were generated in the initiation processes of TiO 2 and V A-044. TiO 2 generated more O 2 •- and less OH compared with V A-044. CS-g-DAC (T) owned the higher ratio of C = N to C-N in molecular structure, the little higher removal efficiency in water treatment and larger floc size than CS-g-DAC (V). The effect of charge neutralization of CS-g-DAC (T) and CS-g-DAC (V) were close. TiO 2 possessed the potential to substitute the traditional photoinitiator in synthesis of organic polymer flocculants and improved the molecular structure and flocculation efficiency of flocculants. [ABSTRACT FROM AUTHOR]

[Display omitted] • A hybrid flocculant with the advantages of both inorganic and organic flocculants was prepared. • Kaolin can improve TiO2-NPs removal rate and promote the density and particle size of flocs. • Humic acid has an inhibitory effect on coagulation with formation of loose and small flocs. • PAC-CA exhibits high-efficiency coagulation removal performance for metal nanoparticles. A hybrid flocculant, PAC-CA, with the advantages of inorganic and organic flocculants, was prepared, and the coagulation behavior and floc characteristics of PAC-CA for removing titanium dioxide nanoparticles (TiO 2 -NPs) under different conditions were studied. The effects of monomer mass ratio, initiator concentration, hydroxyl aluminum ratio, reaction temperature, and polymerization time on the coagulation performance for TiO 2 -NP removal were studied. PAC-CA was characterized through SEM, FT-IR, TG-DSC, XRD, XPS, and Ferron complex colorimetric characterization. The characterization results showed that PAC-CA was successfully copolymerized using AlCl 3 , carboxymethyl chitosan, and acrylamide. The high content of Alb in PAC-CA helped improve the coagulation performance. When the dosage was 30 mg/L, the pH was 8, the stirring intensity was 200 s−1, and the settling time was 30 min, the optimal removal rates for TiO 2 -NPs and turbidity were 87.30% and 91.72%, respectively. Kaolin could effectively improve the TiO 2 -NP removal efficiency and promote the density and particle size of flocs. Humic acid exerted an inhibitory effect on coagulation efficiency with loose and small flocs. [ABSTRACT FROM AUTHOR]

• Novel functionalized chitosan flocculants are successfully synthesized. • Flocculation conditions for reaching high removal efficiencies are optimized. • Characterization results provided empirical evidence for existence of chelating groups. • "3E" triangular model was used to evaluate its flocculation-chelation properties. • Flocculation-chelation capacity profile indicated multiple potential applications. In order to effectively remove the dissolved heavy metals and the heavy metals on the colloidal particles during the flocculation process, a novel dual-functional chitosan flocculant CMCTS-g-P(AM-CA) is prepared by ultraviolet light-initiated graft polymerization using CMCTS, AM, and ammonium dithiocarbamate. The main influencing factors of monomer concentration, monomer ratio, pH value, photoinitiator concentration, and illumination time are investigated on the basis of intrinsic viscosity, grafting rate, and grafting efficiency of CMCTS-g-P(AM-CA). Characterization results provided empirical evidence for existence of chelating groups. In addition, CMCTS-g-P(AM-CA) was applied to treat the simulated heavy metals and electroplating wastewater. The effect of CMCTS-g-P(AM-CA) dosage, pH value, and reaction G value on flocculation efficiency was also explored. After the two-stage flocculation, the residual concentration of Ni(II), COD, and turbidity of actual electroplating wastewater decreased to 0.96 mg/L, 93.00 mg/L, and 1.71 NTU after flocculation tests at optimal condition, respectively. Finally, the "3E" triangular evaluation model is established and applied to evaluate the flocculation performance of CMCTS-g-P(AM-CA) on the actual heavy metal wastewater further, thereby proving its excellent chelation flocculation performance. [ABSTRACT FROM AUTHOR]