Band gap-tunable potassium doped graphitic carbon nitride with enhanced mineralization ability was prepared using dicyandiamide monomer and potassium hydrate as precursors. X-ray diffraction (XRD), N2 adsorption, UV-Vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared catalysts. The CB and VB potentials of graphitic carbon nitride could be tuned from -1.09 and +1.56 eV to -0.31 and +2.21 eV by controlling the K concentration. Besides, the addition of potassium inhibited the crystal growth of graphitic carbon nitride, enhanced the surface area and increased the separation rate for photogenerated electrons and holes. The visible-light-driven Rhodamine B (RhB) photodegradation and mineralization performances were significantly improved after potassium doping. A possible influence mechanism of the potassium concentration on the photocatalytic performance was proposed.

With the exploration and development of natural gas gradually extended to the deep sea, low-temperature and high-pressure environmental conditions and long-distance transportation make flow assurance engineers have to consider the impact of the formation and blockage of natural gas hydrates on the flow stability in the pipeline. Therefore, an inadequate understanding of the hydrate formation and plugging mechanism in a gas-rich (gas-dominant) system has become a serious obstacle to the prediction of hydrate formation and implementation of blocking prevention and control strategies. To this end, this review has conducted a comprehensive review of recent experimental investigations into hydrate formation and blockage in gas-rich systems in flow loop devices, and the physical models to characterize the clogging mechanism of hydrates established by previous scholars were summarized. In addition, the three flow patterns of the gas-rich system were divided, and the hydrate deposition mechanism corresponding to each flow pattern and the prediction model of the deposition layer thickness was summarized. Eventually, the natural gas hydrate mitigation and prophylaxis and restrain strategies used in the process of deep-sea natural gas transportation were summarized, including advantages and disadvantages of natural gas dehydration, changing the gas flow rate, and adding chemical inhibitors. The advantages and feasibility of an under-inhibited system and changing the gas flow rate for the management and prevention of hydrate blockage were emphasized. The conclusion can improve the safety index of natural gas development and transportation operations and reduce the output loss of natural gas energy and economic loss of hydrate anti-blocking.

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