Surface-alkalinization over g-C3N4 was realized by an in-situ synthesis approach of introducing KCl and NH4Cl during the polymerization of melamine. The characterizations of Fourier transform-infrared spectrum, X-ray photoelectron spectrum, and electron spin resonance spectrum over the sample synthesized in presence of KCl/NH4Cl and other reference samples indicated that the K ions played an essential role in breaking the periodic chemical structure of g-C3N4 and meanwhile the trace amount of H2O in melamine could supply OH ions to graft hydroxyl groups. The NH4Cl mainly contributed to exfoliation of layered g-C3N4 particles and pushing negative shift of conduction-band level based on the measurements of BET surface area and valence-band X-ray photoelectron spectrum. An optimal sample, g-C3N4-KCl/0.1gNH4Cl (CN-KCl/0.1gNH4Cl), achieved a more than 14-fold enhancement in photocatalytic H2 evolution under visible-light irradiation compared with the pristine g-C3N4. The enhanced photocatalytic efficiency could be attributed to that the surface hydroxyl groups and the more negative conduction-band level can promote separation of photocarriers and offer a stronger potential for water reduction, respectively.

MnO 2 with different crystallographic forms (R, γ) and morphologies (needles, rods, and spindles) was fabricated via a facile quick-precipitation procedure at a low temperature (about 83 °C) without using any templates or surfactants. The proposed mechanism is focused on the different reaction parameters that affect the behaviors of MnO 6 octahedron units (basic structural framework of MnO 2 ), which then exert an influence on the formation and stack of nuclei in the crystal growth process. Specific capacitances (C s ) calculated according to the area of the cyclic voltammograms (CV) curves were 233.5, 83.1 F 3 g -1 for the needle-and 95.5, 29.3 F 3 g -1 for the spindle-like products at the scan rate of 5, 100 mV 3 s -1 , respectively. The C s of needle-like samples calculated by discharge curves at the current density of 2 mA 3 cm 2 is 209.8 F 3 g -1 , close to the value calculated by CV curves at the scan rate of 5 mV 3 s -1 . This methodology facilitates us to synthesize MnO 2 with discrepant one-dimensional (1D) nanostructures via a quick, simple, and mild route and may be readily extended to the preparation of many other oxide nanoparticles.

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