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Waste fiberboards were used to produce N, O co-doped carbon dots (CDs) by acid etching method. The graphene hydrogels decorated with N, O co-doped CDs (GCD) were synthesized via hydrothermal method and optimized through different mass ratios. The optimal composite electrode exhibited a high specific capacitance of 335.1 F g −1 at 1 A g −1 , and a good mechanical flexibility with about 90.6% capacitance retention after 500 bending/unbending cycles. Furthermore, the assembled flexible supercapacitor owned an ideal cycling stability of 83.4% after 10000 charge/discharge cycles at 5 A g −1 . Such results demonstrated that N, O co-doped CDs played an essential and unique role in composite graphene hydrogel for improving the electrochemical performance of the flexible supercapacitor.

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AbstractA novel amphoteric polyacrylamide (PDAA) was prepared by inverse emulsion polymerization. The influence of its cationic degree and molecular weight on retention property was discussed. Then, the chemical structure and micromorphology of the obtained PDAA were characterized by Fourier infrared spectrum (FTIR), NMR hydrogen spectrum (1H NMR), gel permeation chromatography (GPC), and scanning electron microscope (SEM). Finally, the synergistic retention effects of polydimethyldiallylammonium chloride (PDADMAC), cationic starch (CS), cationic guar gum (CHPG), cationic chitosan (CTS), and polyamine (PA) on the novel PDAA were investigated. The results showed that the optimum cationic degree and molecular weight of PDAA were 25% and 4 million, respectively. The chemical structure of PDAA was confirmed by FTIR, 1H NMR, and GPC. SEM showed that the particle size of PDAA was between 150 and 600 nm, and the particles were very stable because no broken particles were found. In addition, most of the five cationic polymers have good synergistic retention effect on PDAA, and the order of synergistic effect was PDAA/PDADMAC > PDAA/CTS > PDAA/CS > PDAA/CHPG > PDAA/PA.

With the ever-increasing usage of recycled fibers, dry-strength agents play an increasingly important role in the papermaking industry. In this study, a new kind of dry-strength agent (CMS-g-PAM) was developed via grafting polyacrylamide onto carboxymethyl starch (CMS). Effects of the operation conditions, including the CMS-g-PAM dosage, polyaluminium chloride (PAC) dosage, and pH value of pulp system, on the properties of the paper were investigated. The contrasting effects when comparing the CMS-g-PAM and CMS were also researched. The results indicated that CMS-g-PAM had a beneficial effect on the paper properties. Compared to the control sample, when 1% CMS-g-PAM was added, the tensile index, burst index, and folding endurance of handsheets displayed noticeable increases of 38.2%, 34.7%, and 97.7%, respectively, and these properties were increased by 27.4%, 17.2%, and 46.6% when compared with the CMS-treated sample of this addition level. Scanning electron microscopy images showed that the bonding between fibers of the paper became tighter after using the CMS-g-PAM. The results demonstrated that CMS-g-PAM can be used as an effective dry-strength agent.