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A photocatalysis based g-C3N4 system is a green and eco-friendly method for hydrogen production, but limited activity of g-C3N4 is undesirable. Presently, most of the modification strategies for the g-C3N4-based photocatalytic system are centered on doping and heterojunction engineering outside the bulk phase, and little consideration is given to functional group modification within the bulk phase. Herein, surface C-coupled hydroxylated g-C3N4 photocatalysts for efficient H2 evolution are presented. A C-coupled hydroxylation process is proposed through the reaction of formaldehyde with the unsaturated carbon in the g-C3N4 framework. Compared to pristine g-C3N4 photocatalysts, the surface C-coupled hydroxylated g-C3N4 photocatalyst exhibited over 11.18 times more photocatalytic efficiency for H2 production, and impressive apparent quantum yield. The experimental findings and theoretical calculations reveal that the morphology, photo-response features, and crystal structure are maintained after the introduction of C-coupled hydroxylation on the g-C3N4 surface, but the H2O adsorption and H2 production efficiency of g-C3N4 are significantly increased due to excellent photoinduced carrier migration efficiency. Therefore, the functional modification of g-C3N4 photocatalysts with C-coupled hydroxylation is highly favorable. This work could offer a new and useful protocol for designing highly efficient functional photocatalysts from a structural modification perspective. [ABSTRACT FROM AUTHOR]

The combination of nitrogen and phosphorus compounds has synergistic flame retardant effect, but the addition of low phosphorus content compounds is large, which affects the mechanical properties of polymers. Phosphorus ammonium polyphosphate (APP) with high phosphorus content and graphitic carbon nitride (g-C3N4) doped with SiO2 were used for the flame retardant (CN-Si-APP) of polyamide 6 (PA6). CN-Si-APPs with different APP/CN mass ratio (1, 2.5 and 4) and dosage (7 and 12 wt%) were blended with PA6 via a twin-screw extruder, and their flame retardancy was investigated by limiting oxygen index (LOI), UL-94 test, muffle furnace carbonization test and raman spectroscopy. When only APP added, the coefficient of water absorption (CWA) of composites increased and its tensile strength greatly reduced by nearly 37.1% to 35.39 MPa. The addition of g-C3N4 inhibited the water absorption. When the addition dosage is 7%, the CWA of PA6/APP, PA6/CN-Si-APP2.5, PA6 and PA6/CN were 11.1, 6.86, 5.78 and 4.6%, respectively. SiO2 effectively improved the dispersion of g-C3N4 and the mechanical properties of composites. Thermogravimetric analysis (TGA) showed that the char residue of PA6 composites was improved significantly. The composite with 7 wt% CN-Si-APP4 passed the UL-94 V-0 rating. The LOI value and graphitization degree (ID/IG) of PA6/12 wt% CN-Si-APP2.5 reached 28.7% and 2.93 respectively. Under the same dosage, the graphitization degree of CN-Si-APP2.5 (3.51) was higher than that of g-C3N4 (3.98). The barrier protection of g-C3N4, catalytic effect of APP and SiO2 crosslinking network promoted PA6 to form a dense and stable char layer, which protected PA6 composites from the flame. The strategy of synergistic flame retardant in this paper provides a valuable solution for reducing the amount of flame retardant. [ABSTRACT FROM AUTHOR]

The efficiency of Ni(II) removal from electroplating wastewater is highly correlated with different adsorption materials. A Ca-Si activated mineral adsorbent (CSAM) and two ion-exchange resins (732 and D152) were compared. The adsorption of Ni (II) by three materials is spontaneous and endothermic, and their adsorption capacities are similar (48.66–65.36 mg/g at 318K), but the dosage of CSAM is less (1.0 g/L for 50 mg/L Ni(II)), its adsorption is faster (<5 min) and pH range is wider (2–7). 10% NaCl, 1 mol/L HCl and 10% NaCl +1 mol/L HCl were used as desorbent agents, and CSAM exhibited an extremely low desorption rate (1.49–3.41%). The smaller separation factor (close to 0) and XPS analysis showed that the Ni(II) adsorption on CSAM was an irreversible chemical process, which was different from the three-stage adsorption of resins. The treatment of two kinds of electroplating wastewater with high and low concentration showed that CSAM not only had a higher Ni(II) removal rates (>98.4%), but also could efficiently remove Cu(II) (>98%), total-chromium (>79%) and COD (>66%). The treatment of Ni(II) containing electroplating wastewater with ion-exchange resins is greatly affected by the complexing agent. CSAM is more suitable for the treatment of electroplating wastewater containing various metals and organic matters. [ABSTRACT FROM AUTHOR]

To improve the flame retardancy of PA6/PA66 copolymer, a phosphorus‐nitrogen flame retardant DDP‐M was successfully synthesized via melt condensation reaction between 2‐[(5‐oxo‐6H‐phosphanthridin‐5‐yl)methyl]butanedioic acid (DDP) and melamine (Mel). Its structure, product composition, and thermal stability were characterized by FTIR, nuclear magnetic resonance spectroscopy (NMR), matrix‐assisted laser desorption and ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS), and thermogravimetric analysis (TGA). The results suggested that DDP‐M was a hybrid flame retardant. A series of flame‐retardant PA6/PA66 composites were prepared by melt extrusion. Their thermal stability and flame retardancy were assessed by differential scanning calorimetry (DSC), TGA, limiting oxygen index (LOI), and vertical burning test (UL‐94). The combustion behavior demonstrated that DDP‐M can effectively improve flame retardancy, achieving 32% of LOI value and UL‐94 V‐0 rating with only 9 wt.% addition. No melt dripping was accomplished by adding 12% DDP‐M. The high dose (15%) harmed the flame‐retardant properties. The results of pyrolysis gaseous productions analysis and residual carbon analysis revealed the flame‐retardant mechanism of DDP‐M was a synergistic effect of melamine inducing gaseous phase flame retardancy and highly condensed P‐N char layers inducing condensed phase flame retardancy. The composites retained good mechanical properties due to the good dispersibility and compatibility between polyamide and DDP‐M. [ABSTRACT FROM AUTHOR]

Flame‐retardant polyamide 6 (PA6) was prepared by an inorganic‐organic composite (MCN or MgO/g‐C3N4) synthesized by incorporating magnesium oxide (MgO) combined with graphitic carbon nitride (g‐C3N4). As compared to g‐C3N4, MCN possessed a laminate structure, more holes, and a larger specific surface area. The addition of MCN could effectively improve the flame retardancy and mechanical properties of PA6 due to its better compatibility and dispersion in the PA6 matrix. When the addition of MCN was 20 wt%, the vertical combustion performance of the PA6/MCN sample reached flammability rating V‐0 (UL‐94) and the limiting oxygen index (LOI) was up to 32.1%. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) revealed that the introduction of MCN efficiently enhanced thermal stability of PA6. The morphologies of the char residue observed by scanning electron microscopy (SEM) verified that MCN promoted the formation of sufficient, compact, and homogeneous char layers on the composite's surface during burning. Thus led to increase the char layer strength and improve the flame retardancy of PA6. The thermogravimetric analysis/infrared (TG‐IR) revealed the gas‐phase retardancy mechanism of MCN. Compared with PA6/g‐C3N4, PA6/MCN showed better mechanical properties in terms of flexural strength and tensile strength. [ABSTRACT FROM AUTHOR]

A novel, three-dimensional material of g-C3N4/MgO was prepared by pyrolysis method. The adsorption behavior for Pb(II) onto g-C3N4/MgO was systematically investigated. The adsorption experiments confirmed that the g-C3N4/MgO exhibited remarkable adsorption performance owing to its rough morphology and abundant active sites on the surface. The maximum adsorption capacities for Pb(II) reached to 220.3, 226.2 and 235.1 mg/g at 308 K, 318 K and 328 K, respectively. The optimum adsorbent dosage was 1.0 g/L. The adsorption kinetics and isotherm could be well described by the pseudo-second-order model and Langmuir isotherm model, respectively. The adsorption process was spontaneous and endothermic. [ABSTRACT FROM AUTHOR]