Adsorption of Cr(VI) on Cross‐Linked Chitosan Beads

Abstract

A possibility of Cr(VI) removal by the adsorption method is discussed in the paper. An adsorbent were hydrogel chitosan beads are produced by the phase inversion method (by changing pH). The possibility of removing Cr(VI) ions by both pure chitosan hydrogel and its chelate compounds (chitosan cross‐linked with Cu(II) and Ag(I) ions) was investigated. The adsorption proceeded from the solutions of potassium dichromate and ammonium dichromate (NH₄)₂Cr₂O₇ and K₂Cr₂O₇. The process rates and adsorption isotherms were determined and described by relevant equations. The process rate was described by the pseudo‐ and second‐order equations, and adsorption equilibria by the Langmuir equations. A slight advantageous change in adsorption properties of chitosan beads was revealed after cross‐linking (for chromium concentration up to 10 g/dm³). A maximum adsorption was 1.1 g_Cr/g chitosan. Results of the studies show that chitosan hydrogel proves useful in the removal of Cr(VI) ions, additionally, cross‐linking with Cu(II) and Ag(I) ions has an advantageous effect in the case of low‐concentrated solutions.     

Effect of Water on Adsorption Behavior at Polymer/γ-Fe2O3 Interface

The adsorption behavior of a hydroxylated polymer onto γ-Fe₂O₃ particles in a tetrahydrofuran/water solvent system was investigated. The saturation adsorption of the polymer decreased with an increase in the water content of the solvent system, and the degree of dispersion of the magnetic particles in the paint also decreased. It was shown that the water located not at the interface between the particles and the solution but in the solution. Water interacted with the polymer and increased the radius of gyration of the polymer in solution. Thus, the polymer did not interact with the particles, and the particles were prevented from having a high dispersion.     

Effect of different corundum sources on microstructure and properties of Al2O3–Cr2O3 refractories

Al₂O₃–Cr₂O₃ refractories are completely substitutional solid solutions and exhibit better corrosion and abrasion resistance. To enable the comprehensive utilization of it, the microstructure and properties of Al₂O₃–Cr₂O₃ samples with different corundum sources were investigated in this study. The starting sources of corundum sources included sintered tabular corundum, fused white corundum, or brown corundum with minor impurities of β-Al₂O₃ and TiO₂. The results of mechanical test showed that the introduction of white corundum deteriorates the physical structure, while brown corundum acts in an opposite manner. The optimum bonding strength of the Al₂O₃–Cr₂O₃ brick was reached by combining white and brown corundum, whereby rapid neck growth occurred via surface diffusion during solid-phase sintering.     

Fabrication of mesoporous Cr2O3 with highly distributed α-Fe2O3 and Pt nanoparticles for ultrafast H2 evolution rate

In the present contribution, p-n type heterojunction α-Fe₂O₃/Cr₂O₃ S-scheme system photocatalyst has been fabricated utilizing a sol-gel approach with assisted nonionic surfactant for a highly effective H₂ evolution rate under visible illumination. Pt NPs have been reduced by photodeposition during the photocatalytic reaction to collect Pt@α-Fe2O3/Cr2O3 finally. XRD analysis of Fe₂O₃/Cr₂O₃ nanocomposites verified the construction of Fe₂O₃ and Cr₂O₃ with rhombohedral phases. TEM images of Cr₂O₃ NPs were almost spherical and uniform in shape and size (20 ± 5 nm), and very small Fe₂O₃ NPs (3-5 nm) were distributed on the mesoporous Cr₂O₃ networks. The obtained α-Fe₂O₃/Cr₂O₃ photocatalyst exhibited noteworthy photocatalytic H₂ evolution with high efficiency and stability for 45 h. Interestingly, the photocatalytic H₂ evolution rate gradually boosted with the extent of Fe₂O₃ percentage up to 15% and its rate of 2215.4 μmol g^-1h^-1, which was fostered 7.25 folds larger than that of Cr₂O₃ NPs (305.7 μmol g^-1h^-1). The enhancement H₂ evolution rate of Fe₂O₃/Cr₂O₃ photocatalyst in comparison with bare Cr₂O₃ NPs was ascribed to facilitate the separation of photocarriers and existing considerable reactive sites. In addition, constructing n-type Fe₂O₃ and p-type Cr₂O₃ with close contact is essential in improving the H₂ evolution rate. The possible photocatalytic mechanism over Fe₂O₃/Cr₂O₃ nanocomposite was addressed based on electrochemical measurements. The construction of the S-scheme system of Fe₂O₃/Cr₂O₃ nanocomposite could be suggested to improve the separation of photocarriers through optimal transfer channels owing to the formation of synergistic characteristics. Our results provide avenues for constructing stable photocatalysts with high efficiency for H₂ evolution through visible exposure.     

氧化硅/α-Fe2O3多孔结构的制备及Cr(Ⅵ)吸附性能

制备多孔结构是提高材料对重金属离子吸附能力的一种有效方法.利用stober法制备了氧化硅/β-FeOOH核壳结构,研究了原料比例(硅源和氨水的比例)和包覆次数对氧化硅层厚度的影响.再将氧化硅/β-FeOOH核壳结构在500℃煅烧,得到了具有优异吸附能力的氧化硅/α-Fe2O3多孔结构.对比分析了氧化硅/β-FeOOH核壳结构和氧化硅/α-Fe2O3多孔结构对Cr(Ⅵ)离子的吸附动力学和平衡吸附规律.研究了氧化硅层的厚度对重金属离子吸附性能的影响,氧化硅层厚度为50 nm的氧化硅/α-Fe2O3多孔结构对Cr(Ⅵ)离子表现出优异的吸附能力.     

Magnetic properties of fluffy Fe@α-Fe2O3 core-shell nanowires

Novel fluffy Fe@α-Fe₂O₃ core-shell nanowires have been synthesized using the chemical reaction of ferrous sulfate and sodium borohydride, as well as the post-annealing process in air. The coercivity of the as-synthesized nanowires is above 684 Oe in the temperature range of 5 to 300 K, which is significantly higher than that of the bulk Fe (approximately 0.9 Oe). Through the annealing process in air, the coercivity and the exchange field are evidently improved. Both the coercivity and the exchange field increase with increasing annealing time (T_A) and reach their maximum values of 1,042 and 78 Oe, respectively, at T_A = 4 h. The magnetic measurements show that the effective anisotropy is increased with increasing the thickness of theα-Fe₂O₃ by annealing. The large values of coercivity and exchange field, as well as the high surface area to volume ratio, may make the fluffy Fe@α-Fe₂O₃ core-shell nanowire a promising candidate for the applications of the magnetic drug delivery, electrochemical energy storage, gas sensors, photocatalysis, and so forth.     

沉淀法制备α-Fe2O3纳米晶

研究了以FeCl3·6H2O和FeSO4·7H2O为源物质,用均相沉淀法和直接沉淀法制备α-Fe2O3纳米晶粉体,利用TEM、XRD、BET、H2-TPR手段对样品进行了表征.实验结果表明,均相沉淀法所制得α-Fe2O3粉体晶粒尺寸为20nm左右,比表面积大,反应性能好;直接沉淀法所制得粉体晶粒尺寸为80nm左右,比表面积小,反应性能相对差.     

爆炸法合成纳米α-Fe2O3

以微米级还原铁粉为反应原料,通过爆炸法合成了纳米级α-Fe2O3粉体。研究了炸药种类、炸药与铁粉的配比以及冷却介质对合成粉体特性的影响,并用激光粒度分析仪、X射线衍射、透射电镜等手段对产物进行了表征,同时对爆炸反应场的作用机理进行了初步探讨。结果表明：选择负氧平衡指数在-0．59到-0．61之间的混合炸药并控制铁粉和炸药的质量比在70：30到80：20之间,可以制备出粒度为40～50nm、纯度在99％以上的α-Fe2O3粉体。爆炸场的作用机理一方面在于爆炸产生的气体以及高温高压场为纳米粒子的合成和相转变提供了基本的物质和能源;另一方面负氧平衡炸药在爆炸时产生的类气态自由碳在纳米粒子表面沉积,发挥了空间位阻效应,阻止了纳米粒子的生长和团聚。     

α-Fe2O3纳米粉体的掺杂研究

采用溶胶-凝胶法制得Y2O3-α-Fe2O3（W（Y2O3）=0～7％）纳米粉体材料,利用透射电子显微镜对粉体的粒径和形貌进行了观测;利用XRD对产品的物相进行了分析．结合谢乐公式对晶体原始尺寸和晶胞进行了计算：对产品的干凝胶原粉做了TG-DTA分析以研究其热稳定性和相变温度。结果表明：合成的产物颗粒呈圆球形．粒径细小。其中W（Y2O3）=5％的α-FeO3纳米粉体粒径最小,达到22nm。     

纳米α-Fe2O3粒子的湿法制备

综述了近年来国内外纳米α-Fe2O3粒子的湿法制备.主要介绍了沉淀法、水解法、水热法、溶胶-凝胶法和微乳液法的基本原理和应用,最后讨论了纳米α-Fe2O3粒子制备方法的发展方向.     

制备α-Fe2O3纳米粒子的研究进展

介绍了纳米α—Fe2O3的特性,综述了纳米α-Fe2O3的主要制备方法,其中包括：沉淀法、溶胶-凝胶法、强迫水解法、胶体化学法、微乳液法、水热法等。详细介绍了各种制备方法的特点,研究进展;并且结合作者的研究工作,指出了纳米α—Fe2O3制备方法的发展趋势。     

Adsorption separation of CO2, CH4 and N2 on β-zeolite with different SiO2/Al2O3 ratios

采用体积法在273 K和303 K温度下对CO2、CH4和N2在不同硅/铝比的β沸石上的吸附分离性能进行了研究。实验结果表明,Langmuir-Freundlich模型能够较好地拟合吸附实验数据;同一样品上,CO2的吸附量要大于CH4和N2的吸附量;随着硅铝比的减小CO2的吸附量增加,而硅/铝比对CH4和N2的吸附量的影响较小。通过结合Virial方程计算CO2、CH4和N2在不同硅/铝比β沸石上的亨利定律常数和吸附选择性,发现所研究样品对CO2/CH4和CO2/N2均具有很高的吸附选择性,随着样品硅/铝比的减小,CO2/CH4和CO2/N2的吸附选择性显著增加,说明较低硅/铝比β沸石有利于分离CO2。用Clausius-Clapeyron方程求得CO2、CH4和N2在不同硅/铝比的β沸石上的吸附热与吸附量无关,表明β沸石是一种表面势场均匀的吸附剂。     

Influence of annealing treatment on magnetic properties of Fe2O3/SiO2 and formation of ε-Fe2O3 phase

Magnetic properties of Fe₂O₃/SiO₂ samples were studied after being produced by sol-gel synthesis and formation of ε-Fe₂O₃ polymorph. Samples were thermally treated, using different annealing temperatures and annealing times. The size and morphological characteristics of the iron oxide nanoparticles were examined using a TEM microscope. We used the “ellipticity of shapes”, which is a measure of how much the shape of a nanoparticle differs from a perfect ellipse, in order to quantitatively describe morphological properties of nanoparticles. Coercivity measurements were used to identify and monitor the formation of the epsilon-iron oxide phase during the thermal treatments (annealing). Coercivity values were in the range from 1.2 to 15.4 kOe, which is in accordance with previous experience regarding the existence of ε-Fe₂O₃. We have determined the optimal formation conditions for the ε-Fe₂O₃ polymorph (t=1050 °C for 7 h, H_C=15.4 kOe), as well as the narrow temperature interval (1050–1060 °C) in which the polymorph abruptly vanished (H_C=2300 Oe), on the basis of results of the magnetic properties. The threshold temperature for the ε-Fe₂O₃ phase transformation was measured as 1060 °C. We found that different annealing temperatures and annealing times significantly affected magnetic properties of the examined samples.     

Effects of Cr2O3 on Properties of Alumina—spinel Castable

The effects Cr2O3 on properties of alumina-spinel castable has been discussed in this paper,The results show that modulus of rupture(MOR) and cold crushing strength(CCS) of the alumina-spinel castable can be improved when Cr2O is added to this material.At higher temperature,Cr2O3 moves into the melt and raises its viscosity,forming high creep resistance bonding phase,so the thermal shock resistance and slag corrosion resistance are improved.     

Effect of a Bi–Cr–O synthetic multi-phase on the microstructure and electrical properties of ZnO–Bi2O3 varistor ceramics

ZnO–Bi₂O₃–MnO₂ (ZBM)-based varistors were fabricated via doping a novel synthetic multi-phase (SMP) additive produced by calcining the mixture of 18Bi₂O₃·Cr₂O₃ at a given temperature. The effects of the SMP on the microstructural and electrical properties of ZBM varistors were investigated. It was found that the SMP dopant was a compound crystalline phases including Bi–Cr–O phases (Bi_7.38Cr_0.62O_12+x and CrBi₁₈O₃₀) and small amounts of Bi₂O₃ rather than a synthesized polycrystal. The Bi–Cr–O phases were not emerged for samples with x=1, indicating that the amount of it is tiny and the small Bi₂O₃ may accelerate ZnO grain growth. With more SMP doping (x>1) in the ZBM ceramics, it acted as a barrier inhibiting grain growth. For samples with x=5, excellent electrical properties were obtained: the nonlinear coefficient α increased up to 50.19 corresponding to the highly barrier height of 2.62 eV; the leakage current I_L reduced to 0.3 μA. The dielectric constant ε_a is proportional to the ratio of the grain size d to the thickness of the depletion layer width t, which explained the ε_a increased at f=1 kHz for the samples with x=1 and 5. The improvement of the electrical properties can be explained by the oxygen absorption mechanism.     

铁基原位α-Fe2O3的制备与表征

研究了铁基原位α-Fe2O3的制备方法,采用SEM、XRD分析手段对铁板在马弗炉中于600℃、不同氧化气氛和不同煅烧时间下的表层氧化物进行表征。结果表明纯铁板在富氧气氛下煅烧1h的表层氧化物含有α-Fe2O3,形状为叶片状,粒径为800~900 nm,采用拉曼光谱进一步分析表层氧化物,得到表层氧化物的顶层是单一的α-Fe2O3;中间层的主要成分是Fe3O4,同时含有少量γ-FeOOH和α-Fe2O3。     

α-Fe2O3纳米材料的制备及性能研究

以氯化铁(FeCl3·6H2O)为铁源,以十六烷基三甲基溴化铵(CTAB)为表面活性剂,采用水热法制备了准立方体氧化铁纳米材料.所得样品用XRD、SEM及SQUID-VSM等手段进行了表征.结果表明,所得氧化铁纳米材料为边长约700 nm的准立方体,其剩余磁感应强度为0.07 emu/g,矫顽力为1800 Oe,表现出一定的铁磁性.     

水热法制备均分散α-Fe2O3纳米粒子

系统地研究了以Fe(NO3)3为原料,水热合成α-Fe2O3纳米粒子时,前驱物pH值对产物形貌的控制作用.实验结果显示,以Fe(NO3)3为前驱物直接进行水热处理,所得产物形貌为片状;如果Fe(NO3)3溶液用氨水中和形成Fe(OH)3凝胶后,再调节不同的pH值作前驱物,经水热处理所得产物均为单晶粒子,且在不同的pH值下,粒子形貌明显不同:当pH为1时为菱形粒子;pH为3,5时粒子形貌为近球形多孔结构;pH为7时为菱形粒子;pH为9时粒子形貌为近球形、无孔结构.同时分析了在水热条件下前驱物pH值对产物粒径的影响,另外还讨论了反应体系中存在的电解质对α-Fe2O3生成速率的影响机理.     

超声化学法制备纳米α-Fe2O3粉体研究

在超声波反应器中,以工业副产物七水合硫酸亚铁(FeSO4.7H2O)和碳酸氢铵(NH4HCO3)为原料,制备出α-Fe2O3纳米粉体。采用XRD,TEM,TG-DTA等测试手段对样品进行表征,实验所制得的α-Fe2O3纳米粒子晶型为球形,平均粒径为50 nm,粒度分布范围较窄且单分散性好。文章探讨了超声波反应时间对α-FeOOH形成的影响,并比较了在超声波作用下和机械搅拌作用下形成纳米α-Fe2O3的差异,结果为超声波反应生成α-FeOOH,时间以1 h为宜。反应时间缩短5倍。