微波辐射-KOH活化兰炭粉制备活性炭

研究了以兰炭粉为原料,KOH为活化剂,采用微波辐射法制备活性炭的可行性。探讨了微波功率、碱炭质量比和活化时间对活性炭吸附性能的影响。同时采用美国ASAP-2020吸附仪测定了所制备活性炭的N2吸附脱附等温线和孔径分布,采用红外光谱分析了样品的表面官能团。结果表明:微波功率为700 W,碱炭质量比为3,活化时间为15 min工艺条件下制得的活性炭碘吸附值为694.5 mg/g,比表面积为513.62 m2/g,总孔容为0.510 3 cm3/g,平均孔径为3.973 8 nm,该活性炭为中孔型。以兰炭粉为原料,传统加热和微波加热制备的活性炭红外光谱图其峰形基本一致,只是峰强不同。     

氢氧化钾固碱节能技改项目安全措施方案设计

以氢氧化钾固碱工艺节能技改项目为研究对象,简述了固碱工艺节能技改方案,在此基础上从物质的危险特性、生产过程的危险性等方面对该项目可能存在的危险、有害因素进行了辨识,对新工艺的安全生产保障条件进行了分析。并从常规安全措施、自动控制和工艺联锁报警系统等方面提出有针对性的安全措施方案,以期达到提高氢氧化钾固碱工艺节能技改项目的本质安全化水平、减少事故的发生、确保安全发展的目的。并以此为范例,试图为其他同类企业的节能降耗、安全发展等方面提供参考和思路。     

A periodic array of silicon pillars fabricated by photoelectrochemical etching

A periodic array of silicon pillars was photoelectrochemically fabricated using the two-step etching process with a n-type Si (1 0 0) substrate. Two key factors, backside illumination and anodic bias, were required to obtain a high-aspect ratio macropore array of silicon. It was found that the initial pore could be separated into two different pores when the applied anodic bias was greater than a certain critical value. The pore size of the macroporous silicon with a high porosity was increased by anisotropic etching in an alkaline solution. Due to destruction of the pore sidewalls, KOH etching allowed for the fabrication of silicon pillars on a large-scale wafer with an improved uniformity. The anisotropic etching behavior of KOH solution led to necking of the silicon pillars when the etching time exceeded 60 s.     

KOH活化法制备气体分离用炭分子筛膜

选用KOH为活化剂,利用化学活化法制备炭分子筛膜,考察在热塑性酚醛树脂(PFNR)涂膜液中添加不同质量分数的KOH对炭分子筛膜的影响.结果表明,在炭化过程中,KOH的加入可促进炭分子筛膜孔径的均匀分布,使炭分子筛膜具有发达的孔隙结构.当KOH在PFNR中的添加量从0％增加到4％时,H2的渗透速率由23.68×10-10 mol·m-2·s-1·pa-1提高到28.6×10-10 mol·m-2·s-1·Pa-1;但H2/N2和H2/CH4的分离系数明显下降,分别从471.3下降到147.5、540下降到270.CO2/CH4和O2/N2的分离系数只有轻微下降.     

KOH亚熔盐法分解钛铁矿

以KOH亚熔盐为反应介质,研究了KOH浓度、反应温度与时间、搅拌速率和碱/矿比等因素对钛铁矿在KOH亚熔盐体系中分解率的影响. 结果表明,反应温度、反应时间及KOH浓度为主要影响因素,提高反应温度及KOH浓度均有利于钛铁矿在KOH亚熔盐中的分解,但当反应温度超过260℃时,钛铁矿的分解率又随反应温度的升高而降低;在KOH浓度80%(w)、搅拌速度700 r/min、反应温度260℃、碱/矿质量比5、反应时间180 min的条件下,钛铁矿在KOH亚熔盐中的分解率超过95%. 此外,钛铁矿在KOH亚熔盐中的分解符合未反应收缩核模型,受界面化学反应控制.     

Single Unit-Cell Layered Bi2Fe4O9 Nanosheets: Synthesis,Formation Mechanism,and Anisotropic Thermal Expansion

As an important multiferroic material, pure and low-dimensional phase-stable bismuth ferrite has wide applications. Herein, one-pot hydrothermal method was used to synthesize bismuth ferrite. Almost pure Bi₂Fe₄O₉, BiFeO₃, and their mixture were successfully obtained by controlling the KOH concentration in the hydrothermal solutions. The as-prepared Bi₂Fe₄O₉ products were crystalline with Pbam space group, had nanosheet morphology, and tended to aggregate into nanofloret or random stacking. Each Bi₂Fe₄O₉ nanosheet was a single crystal with (001) plane as its exposed surface. Single unit-cell layered Bi₂Fe₄O₉ nanosheets had a uniform thickness of 1 nm. The surface energies of various (100), (010), and (001) planes were 3.6–4.0, 5.6–15.1, and 1.7–3.0 J m⁻², respectively, in the Bi₂Fe₄O₉ crystal. The formation mechanism and structural model of the as-prepared single unit-cell layered Bi₂Fe₄O₉ nanosheets have been given. The growth of Bi₂Fe₄O₉ nanosheets was discussed. Thermal analysis showed that the Bi₂Fe₄O₉ phase was stable up to 1260 K. The thermal expansion behavior of the Bi₂Fe₄O₉ nanosheet was nonlinear. The thermal expansion coefficients of the ultrathin Bi₂Fe₄O₉ nanosheets on the a-, b-, c-axes, and on the unit-cell volume V were determined, showing an anisotropic thermal expansion behavior. This study is helpful for the controllable synthesis of ultrathin Bi₂Fe₄O₉ nanosheets.     

Creating Pores on Graphene Platelets by Low‐Temperature KOH Activation for Enhanced Electrochemical Performance

KOH activation of microwave exfoliated graphite oxide (MEGO) is investigated in detail at temperatures of 450–550 °C. Out of the activation temperature range conventionally used for the preparation of activated carbons (>600 °C), the reaction between KOH and MEGO platelets at relatively low temperatures allows one to trace the structural transition from quasi‐two‐dimensional graphene platelets to three‐dimensional porous carbon. In addition, it is found that nanometer‐sized pores are created in the graphene platelets at the activation temperature of around 450 °C, leading to a carbon that maintains the platelet‐like morphology, yet with a specific surface area much higher than MEGO (e.g., increased from 156 to 937 m² g^–1). Such a porous yet highly conducting carbon shows a largely enhanced electrochemical activity and thus improved electrochemical performance when being used as electrodes in supercapacitors. A specific capacitance of 265 F g^–1 (185 F cm^–3) is obtained at a current density of 1 A g^–1 in 6 m KOH electrolyte, which remains 223 F g^–1 (156 F cm^–3) at the current density of 10 A g^–1.     

Preparation and CO_2 adsorption properties of porous carbon by hydrothermal carbonization of tree leaves

Porous carbon materials were prepared by hydrothermal carbonization(HTC) and KOH activation of camphor leaves and camellia leaves. The morphology, pore structure, chemical properties and CO_2 capture ability of the porous carbon prepared from the two leaves were compared. The effect of HTC temperature on the structure and CO_2 adsorption properties was especially investigated. It was found that HTC temperature had a major effect on the structure of the product and the ability to capture CO_2. The porous carbon materials prepared from camellia leaves at the HTC temperature of 240℃ had the highest proportion of microporous structure, the largest specific surface area(up to 1823.77 m~2/g) and the maximum CO_2 adsorption capacity of 8.30 mmol/g at 25℃ under 0.4 MPa. For all prepared porous carbons, simulation results of isothermal adsorption model showed that Langmuir isotherm model described the adsorption equilibrium data better than Freundlich isotherm model. For porous carbons prepared from camphor leaves, pseudo-first order kinetic model was well fitted with the experimental data. However,for porous carbons prepared from camellia leaves, both pseudo-first and pseudo-second order kinetics model adsorption behaviors were present. The porous carbon materials prepared from tree leaves provided a feasible option for CO_2 capture with low cost, environmental friendship and high capture capability.     

Evaluation of activated carbon adsorbent for fuel cell cathode air filtration

The effectiveness of a commercial activated carbon modified by KOH (KMAC) was evaluated as adsorbent for purifying NO_x and SO₂, which are the major contaminants in fuel cell cathode air stream. The N₂ adsorption–desorption isotherms of KMAC samples showed that the surface structure of the activated carbon was changed significantly by KOH impregnation. The sample of KMAC with a loading of 10.1% KOH by weight presented the highest adsorption capacities for both NO_x and SO₂, which were 96 mg g⁻¹ and 255 mg g⁻¹, respectively. A pre-exposure of KMAC to CO₂ caused neither effect on the adsorption of NO_x nor on the adsorption of SO₂. KMAC could fully protect a 250 W proton exchange membrane fuel cell (PEMFC) stack from 1100 ppb of NO_x and 250 ppb of SO₂ for about 130 h.