Extraction of silica from fly ash to produce mesoporous silica materials is one of the most important utilization approaches.Mesoporous silica could not be synthesized on a large-scale by conventional sol-gel method.I...Extraction of silica from fly ash to produce mesoporous silica materials is one of the most important utilization approaches.Mesoporous silica could not be synthesized on a large-scale by conventional sol-gel method.In this paper,facile preparation of mesoporous silica with controllable pore structure from fly ash by the template-free process via two steps of mineral phase transformation and selective acid etching was proposed.The influence of crystalline structure and acid etching degree on structure of as-synthesized mesoporous silica materials was revealed,as well as mechanism of crystalline structure transformation and pore structure formation.The results show that mullite and quartz could be transformed into acid-soluble kaliophilite when fly ash reacted with K_(2)CO_(3)at temperature of 800-1100℃.The hexagonal kaliophilite would be transformed into orthorhombic KAlSiO_(4)-O1 phase when the temperature is controlled at 1100℃.Mesoporous silica with specific surface area of 475.93 m^(2)/g and 642.57 m^(2)/g could be synthesized from activated fly ash with kaliophilite and KAlSiO_(4)-O1 phase crystalline structure.By controlling the degree of acid etching,mesoporous silica materials with different pore structures can be obtained.This paper provides a cost-effective and large-scale process for the preparation of mesoporous silica materials with controllable pore structure from solid waste fly ash.展开更多
In this study, controlled-release fertilizers （CRFs） with five different nitrogen release periods were pre- pared by coating large urea particles with polyethylene （PE） membranes under various experimental conditi...In this study, controlled-release fertilizers （CRFs） with five different nitrogen release periods were pre- pared by coating large urea particles with polyethylene （PE） membranes under various experimental conditions. The preliminary and differential solubility rates, release periods, and membrane pore sizes of the obtained CRFs were measured using water immersion, scanning electron microscopy, and mercury porosimetry. For all CRF samples, the median pore diameters of the membranes were equal to 4.5-5.3 nm and pores with sizes smaller than 10 nm accounted for 86-96% of the total pore surface area. The obtained pore diameter distributions differed for the five studied types of CRF, having release periods of 1,2, 4, 6, and 8 months. Thus, for the CRFs with a 1-month release period, the maximum pore diameter reached a magnitude of 4000 nm, while this value did not exceed 30 nm for the CRFs with a release period of 8 months. Hence, we have established a relationship between the release period of CRFs and their effective maximum pore sizes.展开更多
Potassium ion batteries(PIBs)with high-volumetric energy densities are promising for next-generation low-cost energy storage devices.Metallic bismuth(Bi)with a structure similar to graphite,is a promising anode materi...Potassium ion batteries(PIBs)with high-volumetric energy densities are promising for next-generation low-cost energy storage devices.Metallic bismuth(Bi)with a structure similar to graphite,is a promising anode material for PIBs due to its high theoretical volumetric capacity(3763 mA h cm^−3)and relatively low working potential(−2.93 V vs.standard hydrogen electrode).However,it experiences severe capacity decay caused by a huge volume expansion of Bi when alloying with potassium.This study reports a flexible and free-standing Bi nanosheet(BiNS)/reduced graphene oxide composite membrane with designed porosity close to the expansion ratio of BiNS after charging.The controlled pore structure improves the electron and ion transport during cycling,and strengthens the structural stability of the electrode during potassiation and depotassiation,leading to excellent electrochemical performance for potassium-ion storage.In particular,it delivers a high reversible volumetric capacity of 451 mA h cm^−3 at the current density of 0.5 A g^−1,which is much higher than the previously reported commercial graphite material.展开更多
基金supported by the National Natural Science Foundation of China(grant Nos.U21A20321 and 21908138)Shanxi Province Central Government Guided Local Science and Technology Development Fund Project(grant No.YDZJSX2022A004)Shanxi Province Scientific and Technological Innovation Project of Colleges and Universities(grant No.2020L0009).
文摘Extraction of silica from fly ash to produce mesoporous silica materials is one of the most important utilization approaches.Mesoporous silica could not be synthesized on a large-scale by conventional sol-gel method.In this paper,facile preparation of mesoporous silica with controllable pore structure from fly ash by the template-free process via two steps of mineral phase transformation and selective acid etching was proposed.The influence of crystalline structure and acid etching degree on structure of as-synthesized mesoporous silica materials was revealed,as well as mechanism of crystalline structure transformation and pore structure formation.The results show that mullite and quartz could be transformed into acid-soluble kaliophilite when fly ash reacted with K_(2)CO_(3)at temperature of 800-1100℃.The hexagonal kaliophilite would be transformed into orthorhombic KAlSiO_(4)-O1 phase when the temperature is controlled at 1100℃.Mesoporous silica with specific surface area of 475.93 m^(2)/g and 642.57 m^(2)/g could be synthesized from activated fly ash with kaliophilite and KAlSiO_(4)-O1 phase crystalline structure.By controlling the degree of acid etching,mesoporous silica materials with different pore structures can be obtained.This paper provides a cost-effective and large-scale process for the preparation of mesoporous silica materials with controllable pore structure from solid waste fly ash.
基金This work described above was financially supported by National Key R＆D Program of China （No. 2017YFD0200703）, and the General Program of Natural Science Foundation of China （grant number 31572204）. The authors would like to thank Hongying Cai from the Department of Chemical Engineering of Tsinghua Univer- sity for his help with SEM observations and Dongwu Chang from the Department of Thermal Energy Engineering of Tsinghua University for assistance with MP measurements.
文摘In this study, controlled-release fertilizers （CRFs） with five different nitrogen release periods were pre- pared by coating large urea particles with polyethylene （PE） membranes under various experimental conditions. The preliminary and differential solubility rates, release periods, and membrane pore sizes of the obtained CRFs were measured using water immersion, scanning electron microscopy, and mercury porosimetry. For all CRF samples, the median pore diameters of the membranes were equal to 4.5-5.3 nm and pores with sizes smaller than 10 nm accounted for 86-96% of the total pore surface area. The obtained pore diameter distributions differed for the five studied types of CRF, having release periods of 1,2, 4, 6, and 8 months. Thus, for the CRFs with a 1-month release period, the maximum pore diameter reached a magnitude of 4000 nm, while this value did not exceed 30 nm for the CRFs with a release period of 8 months. Hence, we have established a relationship between the release period of CRFs and their effective maximum pore sizes.
基金This work was supported by the National Natural Science Foundation of China(51902176)China Postdoctoral Science Foundation(2018M631462)+1 种基金Guangdong Innovative and Entrepreneurial Research Team Program(2017ZT07C341)Shenzhen Municipal Development and Reform Commission and the Development and Reform Commission of Shenzhen Municipality for the development of the“Low-Dimensional Materials and Devices”Discipline.
文摘Potassium ion batteries(PIBs)with high-volumetric energy densities are promising for next-generation low-cost energy storage devices.Metallic bismuth(Bi)with a structure similar to graphite,is a promising anode material for PIBs due to its high theoretical volumetric capacity(3763 mA h cm^−3)and relatively low working potential(−2.93 V vs.standard hydrogen electrode).However,it experiences severe capacity decay caused by a huge volume expansion of Bi when alloying with potassium.This study reports a flexible and free-standing Bi nanosheet(BiNS)/reduced graphene oxide composite membrane with designed porosity close to the expansion ratio of BiNS after charging.The controlled pore structure improves the electron and ion transport during cycling,and strengthens the structural stability of the electrode during potassiation and depotassiation,leading to excellent electrochemical performance for potassium-ion storage.In particular,it delivers a high reversible volumetric capacity of 451 mA h cm^−3 at the current density of 0.5 A g^−1,which is much higher than the previously reported commercial graphite material.
