Adsorption of Chromium (VI) Using an Activated Carbon Derived from Petroleum Coke Feedstock

This study aims to determine the main adsorption mechanism by which chromium (VI) is adsorbed onto the surface of a petroleum-coke sourced activated carbon, a feedstock not prevalent in current literature. The study also aims to produce an activated carbon adsorbent that is both cost-effective and efficient for the removal of chromium (VI) in neutral waters. The efficacy of thermally-treated petroleum coke-activated carbon and nitrogenated petroleum coke-activated carbon using ammonium chloride is compared to the efficacy of commercially available activated carbon. X-ray photoelectron spectroscopy of the activated carbons was obtained both before and after exposure to chromium (VI) for characterization of the materials and confirmation of chromium adsorption. The thermally-treated and nitrogenated activated carbons showed significant enhancement of chromium (VI) removal compared to the non-treated petroleum coke-activated carbon (22.4 mg/g, 21.9 mg/g, and 17.0 mg/g, respectively). However, there was no significant difference observed between the thermally-treated and nitrogenated materials. This indicates that the nitrogenation of the surface does not improve the adsorption capacity of the activated carbon, but rather the thermal treatment itself. X-ray photoelectron spectroscopy showed a significant increase in the alcohol functional groups on the surface of the activated carbon material as a result of the heat-treatment process; from 16.02 atomic percent in the non-treated activated carbon to 26.3 atomic percent in the thermally-treated activated carbon. The alcohol functional groups present on the surface allow for chromium (VI) to undergo reduction to chromium (III) under a similar mechanism to the well-known Jones Oxidation Reaction where the reduced chromium (III) species are then physisorbed to the surface of the activated carbon. XPS results are consistent with this as the chromium species present on the surface of the adsorbent is primarily Cr(OH)₃ (85.6% in the standard AC and 82.5% in the thermally-treated AC). Pseudo-first-order and pseudo-second-order kinetic modeling of the adsorbents indicate that they follow a pseudo-second-order reaction where the rate-limiting step is the chemical sorption of the adsorbate itself.     

北京市中心商区射频电磁环境测试与分析

城市电磁环境强度的逐渐升高对人体健康和电子系统正常工作构成潜在威胁,为实现对电磁环境状况的快速判别,提出一种电磁环境与人口热力及建筑密度的关联规则挖掘方法. 首先通过两步聚类分别将电磁环境、人口热力、建筑密度数据离散为三种等级,再基于动态阈值FP增长（Frequent Pattern Growth）算法进行规则挖掘,最后筛选出有效的关联规则. 将所提出方法应用于北京城区道路采样的28 424组数据,实验结果表明：人口热力为中、低等级的区域或建筑密度低的区域,电磁环境强度通常低于1.52 V/m;建筑密度高的区域,电磁环境强度通常在1.52～3.50 V/m;而电磁环境强度高于3.50 V/m的情况主要出现在人口热力高的区域. 本文的研究工作为城市电磁环境的快速估计与监测预警提供了新思路和参考.

     

电磁辐射职业危害及防护对策

针对居住环境内电磁辐射在周期性规律中混有较多高频分量,导致传统时序建模方法和神经网络方法预测性能受限的问题,提出了一种小波分解与季节性差分自回归滑动平均（seasonal autoregressive integrated moving average, SARIMA）模型相结合的混合预测方法. 该方法根据辐射数据的时频特性,利用SARIMA模型对小波分解得到的主要周期分量和细节分量进行分层预测,以适应居住环境内多种发射源形成的复杂电磁辐射状况. 实验结果表明,该方法不仅比单一时序建模方法以及神经网络方法具有更高的预测准确度,而且具有更强的异常值适应性与稳定性.     

三面角反射器的高频电磁散射分析

角反射器是一种宽角域的常见无源干扰设备,常被用于保护关键目标. 但传统金属角反射器特性固定,需借助新型电磁材料实现角反射器的特性优化. 有源频率选择表面（adaptive frequency selective surface,AFSS）是在单元间加载一系列可变有源器件而构成的具有可调电磁特性的新型结构. 为拓展角反射器的适用范围、分析电磁材料角反射器的散射特性以更好地保护关键目标,本文设计了一种基于单面AFSS的电控角反射器,并仿真计算分析了该电控角反射器的散射特性. 仿真结果表明设计的电控角反射器的散射特性可灵活调控,即不同偏置电流下AFSS单元可对入射电磁波能量产生不同反射效果;同时验证了该电磁调控角反射器的宽角域特性,其调控角域在方位向、俯仰向均大于60°,实现了基于无源散射体的宽角域实时调控效果. 相较于传统角反射器和平面电磁材料,所设计电控角反射器兼具实时调控性和宽角域特性,拓展了角反射器的应用场景和适用范围.

     

一种新型Ku波段龙伯透镜反射器

本文对传统的龙伯透镜反射器采用有源频率选择表面（active frequency selective surface, AFSS）技术进行电磁结构的设计,用具有吸波/反射可切换的AFSS龙伯透镜反射器代替金属反射板,达到对入射电磁波的反射强度和雷达散射截面（radar cross section, RCS）大小可调、工作状态可切换的主动型龙伯透镜反射器. 仿真结果表明,在X波段内,设计的新型龙伯透镜反射器可实现吸波/反射功能的可切换以及单站RCS可调,大小相差约8 dB. 通过对龙伯透镜AFSS反射器进行实物加工与测试,测试结果和仿真结果较为吻合,实现了龙伯透镜反射器在一定频段内工作状态切换和RCS可调.

     

Mechanical properties and microstructure evolution of KD-SA SiCf/BN/SiC CMCs oxidized at different temperatures

Silicon carbide fiber-reinforced SiC ceramic matrix composites (SiC_f/SiC CMCs) based on a domestic KD-SA SiC fiber were exposed to a wet oxygen atmosphere for 135 h at 800, 1100, and 1300°C. The evolution of the microstructure and mechanical properties of SiC_f/SiC CMCs have been systematically investigated following oxidation. For weight change, CMC-1300 showed the greatest gain (0.394%), followed by CMC-1100 (0.356%) and CMC-800 (0.149%). The volatilization of boron oxide (B₂O₃) combined with the slight oxidation of the SiC matrix at 800°C caused crack deflection and fiber pull-out. The complete dissipation of the interphase could be found when the oxidation temperature increases to 1100°C, generated a fracture surface with brittle fracture characteristics. At 1300°C, crystalline SiO₂ hindered oxygen diffusion, with evidence of fiber pull-out. Based on thermodynamic calculations and microscopic observations, we propose a mechanism to explain the thermal degradation of SiC_f/SiC CMCs. This work offers valuable guidance for the fabrication of SiC_f/SiC CMCs that are suitable for high-temperature applications.     

生物防腐剂的保鲜机理及应用

食品加工、贮运过程中由微生物引起的腐败变质一直是食品保鲜领域所面临的世界性难题。因化学防腐剂的使用所带来的安全隐患越来越不容忽视,安全、高效的生物防腐剂的开发逐渐成为食品保鲜领域的重点。但生物防腐剂作用靶点相对单一、成本较高一直制约其发展。如何合理组合不同的生物防腐剂,在降低单因素强度的基础上实现多靶点协同攻击腐败菌越来越受重视。本文系统梳理以细胞壁、细胞膜、胞内遗传物质及以革兰氏阴性菌细胞外膜层为损伤目标的生物防腐剂,归纳它们的作用方式和在食品保鲜中的应用效果,并对未来的研究重点进行展望,以期能为生物防腐保鲜剂的精准复配提供理论依据。      

粉煤灰基陶瓷膜过滤苹果汁及其污染机理研究

利用统计学方法比较了实验室自制的三种粉煤灰基微滤陶瓷膜对苹果汁的过滤效果,并初步考察了其污染机理。采用不同孔径的膜(2.13、1.25、0.30μm)对苹果汁进行过滤后,苹果汁色度明显改善,澄清度大大提高,同时去除了果汁中容易引起浑浊的蛋白质和多酚,而其它理化性质指标如p H、密度、可溶性固形物含量基本保持不变;三种微滤膜的污染机制各不相同。综合考虑,1.25μm的微滤膜过滤效果最佳。粉煤灰基微滤陶瓷膜对苹果汁过滤具有很好的应用前景。