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Ni2+ rich wastewater has caused critical water contamination, a growing issue of environmental pollution as well as serious threat to aquatic organisms and human health. It is of great significance and urgent to develop a novel and efficient wastewater treatment technology for Ni2+ removal. The efficient removal of Ni2+ by flocculation has always become a hot and focus topic. In this study, a novel chitosan (CS) graft modified flocculants CS-g-P(AM-IA-AATPAC), namely CS-g-PAAI, is prepared by microwave initiation and polymerization, and is applied in the removal of Ni2+. The effects of microwave power, microwave irradiation time, initiator concentration and pH on the CS graft polymerization efficiency and flocculant molecular weight were investigated and optimized, so as to further understand the rules of microwave initiation and CS-g-PAAI graft and polymerization. Various characterization methods indicated the successful grafting and synthesis of CS-g-PAAI. Meanwhile, the structural characteristic results manifested that CS-g-PAAI possessed a good thermal stability, a coarse and porous apparent morphology, and its chemistry and crystal structure was evidently changed and affected after graft polymerization. Compared with CS, PAA and CS-g-PAA, the removal efficiency of Ni2+ by CS-g-PAAI is more exceedingly favorable and desirable. The flocculation effect of Ni2+ by CS-g-PAAI is as high as 86.3% at the optimal condition of pH = 9, flocculant dosage = 4 mg/L, the stirring speed = 400 rpm, and flocculation time = 30 min. Meanwhile, the generated Ni2+ floc size (d 50) and fractal dimension (D f) can reach a high value (d 50 = 339.3 µm, D f = 1.98), which accelerates the sedimentation and separation of the formed Ni2+ flocs. CS-g-PAAI shows excellent flocculation and coordination ability by its powerful coordination groups to strengthen the adsorption and chelating of Ni2+ ions and generate colloidal particles for subsequent flocculation. Then, efficient flocculation was carried out and proceeded through the bridging effect, the concomitant sweeping and netting action. [Display omitted] • CS-g-PAAI with both flocculation and coordination chelating effect was successfully synthesized. • There is a significant synergistic effect between flocculation and coordination chelating. • The introduction of IA can significantly improve the flocculation and removal effect of Ni2+. • 4. The Ni2+ floc particle size and fractal dimension conditioned by CS-g-PAAI are large and desirable. [ABSTRACT FROM AUTHOR]

A development of coagulation-flocculation is to improve flocculation performance of organic polymer flocculants. It is hopefully achieved via optimizing molecular structure of flocculants. Herein, molecular structure of cationic organic polymer flocculants, P(AM-DAC), was regulated through adjusting the length of cationic block on the molecular chain of P(AM-DAC). The effect of block length of P(AM-DAC) on its characteristics, flocculation performances and flocculation mechanisms in water treatment was rarely considered. The moderate template contributed to P(AM-DAC) (10_4:1) possessing the longest cationic block structure, largest molecular weight and best thermal stability compared with other P(AM-DAC). Molecular dynamics (MD) simulation and the flocculation experiments predicted and confirmed that P(AM-DAC) (10_4:1) performed the best in the treatment of colloidal particles and dyes in terms of removal efficiencies and floc characteristics since the centralized cationic block structure enhanced the interaction among P(AM-DAC) (10_4:1) and pollutants and further improved charge neutralization and bridging of P(AM-DAC) (10_4:1). [Display omitted] • P(AM-DAC) with different block lengths were adjusted via various template sizes. • P(AM-DAC) (10_4:1) owned the longest block length as moderate molecular weight of template. • The strong interaction between P(AM-DAC) (10_4:1) and pollutants was confirmed by MD. • P(AM-DAC) (10_4:1) with concentrated cationic blocks had the best flocculation performance. [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]

A novel chelating flocculant with branched architectures, polyacrylamide grafted maleoyl chitosan-mercaptoacetic acid (PAM-g-M(CS-MA)), was successfully fabricated using maleic anhydride as the "bridge" between chitosan and polyacrylamide. The functional groups and structural characteristic information of copolymers were obtained via characterization analysis. Flocculation performance was systematically investigated via purifying a series of simulated wastewater containing Cu or Cd. The properties of the flocs were studied to give in-depth evidences for the role of chelation groups and branched architectures in flocculation. Results indicated that PAM-g-M(CS-MA) showed excellent flocculation capacity for heavy metals in high concentrations and was superior to other chelating flocculants. The maximum flocculation efficiency of Cu (93.90%) and Cd (92.47%) was achieved by PAM-g-M(CS-MA) at pH 7, dosage of 100 mg L−1 and stirring speed of 90 rpm. The flocculation mechanisms of PAM-g-M(CS-MA) were deeply explored through the analyses of floc properties. The strong synergistic chelation of mercapto, carboxyl, amide and hydroxyl groups predominated for the capturing of heavy metals; and the branched architectures facilitated the formation of large and stable flocs via adsorption and bridging-furl effect. This study provided a solid foundation for the fabrication of flocculants for heavy metal wastewater treatment. [Display omitted] • A flocculant with branch architectures (PAM-g-M(CS-MA)) was synthesized. • PAM-g-M(CS-MA) showed low-dosage and efficient in heavy metals removal. • The maximum removal rates of Cu (93.90%) and Cd (92.47%) can be achieved by PAM-g-M(CS-MA). • Relationship between the branch architectures and flocculation performance was built. • Flocculation mechanism is composed by synergistic chelation, adsorption and bridging-furl effect. [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]