The removal of Cr(VI) through polymeric supported liquid membrane by using calix[4]arene as a carrier

In this work, the transport and removal of Cr(VI) were achieved through supported liquid membrane (SLM) by using a 5,17, di-tert-butyl-11,23-bis[(1,4-dioxa-8-azaspiro [4,5]decanyl)methyl]-25,26,27,28-tetrahydroxy calix[4]arene carrier, dissolved in 2-nitrophenyl octyl ether dichloromethane. The studied parameters are the solvent effect in the membrane phase, the effect of carrier concentration, and the acid type in the donor phase. The Celgard 2500 was used as a membrane support. We used the Danesi mass transfer model to calculate the permeability coefficients for each studied parameter. In addition, AFM and SEM techniques were used to characterize the surface morphology of the prepared Celgard 2500 membrane that included the calix[4]arene carrier.     

Synthesis of Various Calix[4]arene Derivatives with Mercaptoalkyl Chains and Their Application in Removing Cr(VI) from Aqueous Solution

Four different mercaptoalkyl-substituted calixarene derivatives (5,11,17,23-tetra-tert-butyl-25,27-bis(3-mercaptopropoxyl)-26,28-dihydroxycalix[4]arene, 25,27-bis(3-mercaptopropoxyl)-26,28-dihydroxycalix[4]arene, 25,27-bis(5-mercaptopentanoxyl)-26,28-dihydroxycalix[4]arene and 5,17-di-tert-butyl-11,23-di-carboxyl-26,28-bis(3-mercaptopropoxyl)-25,27-di-hydroxycalix[4]arene) were synthesized. Their structures were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H and ¹³C NMR spectroscopy, and elemental analysis techniques. Moreover, their extraction capabilities at different parameters such as pH, shaking speed, and shaking time were examined toward dichromate ions. Results implied that all mercaptoalkyl-substituted calixarene derivatives showed an extraction capability toward dichromate anion while the carboxyl-functionalized calixarene-marcapto-alkyl derivative exhibited the highest extraction capability.     

Modelling of Cr(VI) removal from polluted groundwaters by ion exchange

This work reports the viability and modelling of the removal of Cr(VI) from polluted groundwaters by means of ion exchange using the resin Lewatit MP‐64. Feed groundwaters that contained Cr(VI) at an average concentration of 2431 mg dm^?3 and 1187 mg dm^?3 of chloride and 1735 mg dm^?3 of sulfate as main anions were acidified to a pH of 2.0 prior to the removal process. Dynamic experiments were carried out in a fixed bed column with feed waters at flow rates in the range of 2.78 × 10^?7 m³ s^?1 to 5.55 × 10^?7 m³ s^?1. Regeneration was achieved with NaOH (2 mol dm^?3). From the experimental results, the equilibrium of the ion exchange reaction was successfully modelled, obtaining an equilibrium constant (K′_AB) = 44.90. Finally, a mass balance that included mass transfer resistances in the liquid and solid phases was developed and from the comparison between simulated and experimental data the value of the effective intraparticle diffusivity (D_s) was determined as 1.43 × 10^?12 m² s^?1. Copyright © 2004 Society of Chemical Industry     

对叔丁基杯[4]芳烃包合物对聚乳酸结晶过程的影响

以对叔丁基杯[4]芳烃(tBC4)为主体,甲苯、邻二甲苯、间二甲苯、对二甲苯为客体分子,制备4种tBC4包合物tBC4-t、tBC4-ox、tBC4-mx、tBC4-px。考察了tBC4包合物对左旋聚乳酸(PLLA)结晶性能及结晶形态的影响。结果表明,tBC4包合物能将PLLA的结晶峰值温度(T_p)提高近7℃;进一步研究发现几种包合物在经高温后,客体小分子逃逸,样品均改变为相同的晶体结构,因此对PLLA成核有相同的影响;此外,含有成核剂的PLLA球晶尺寸小于空白PLLA的球晶尺寸,成核剂的加入不改变PLLA球晶生长的方式。     

Mechanisms of Cr(VI) removal from water by various types of activated carbons

The removal mechanisms of Cr(VI) from water using different types of activated carbons, produced from coconut shell, wood and dust coal, were investigated in this project. Different types of activated carbons have different surface characteristics. The coconut shell and dust coal activated carbons have protonated hydroxyl groups on the surface (H‐type carbons), while the surface of the wood‐based activated carbon has ionised hydroxyl groups (L‐type carbons). The adsorption kinetics of chromium onto the activated carbons at pH values ranging from 2 to 6 were investigated. It was found that the optimum pH to remove total chromium was 2 for wood‐based activated carbon, while for coconut shell and dust coal activated carbons, the optimum pH was around 3–4. The difference in the optimum pH for different activated carbons to remove Cr(VI) from water can be explained by the different surface characteristics and capacity of the activated carbons to reduce Cr(VI) to Cr(III). © 1999 Society of Chemical Industry     

活性炭对Cr(VI)吸附机理的探讨

根据焦作电厂粉煤灰堆放场引起地下水中Cr(VI)污染的实际情况,在实验室里模拟配制水样,使其接近当地地下水中Cr(VI)浓度,进行活性炭对Cr(VI)的吸附试验。对所得的试验数据进行分析,探讨活性炭的吸附机理。这些工作为处理和修复被污染的地下水提供理论依据,此外,还对去除地下水中Cr(VI)提出合理建议。     

Well-designed ZnIn2S4/TiO2 Z-type heterojunction for efficient photocatalytic reduction of Cr(VI)

ZnIn₂S₄/TiO₂ photocatalyst was obtained by a facile hydrothermal method. Various techniques were used to characterize the ZnIn₂S₄/TiO₂, crystal structure and optical properties of ZnIn₂S₄/TiO₂. Cr (Ⅵ) as highly-toxic pollutant was used as the target reduction product to evaluate the catalytic performance of ZnIn₂S₄/TiO₂ under visible light irradiation. According to the experiment results, the reduction rate of Cr(VI) in the presence of ZnIn₂S₄/TiO₂ reaches 99% within 60 min, which is much better than ZnIn₂S₄ and TiO₂, respectively. At the same time, ZnIn₂S₄/TiO₂ also performs good stability for reduction rate hardly changes after 5 recycling experiments.     

Highly selective separation and recovery of Pd(II) from the automotive catalyst residue with the thiocarbamoyl substituted azothiacalix[4]arene derivative

New ligand, namely, 5, 11, 17, 23-tetrakis-((p-chlorophenyl) azo)-25,26,27,28-tetrakis ((dimethylthio carbamoyl)oxy) thiacalix[4]arene (CADTTCA), has been investigated for separation and recovery of Pd(II) through solvent extraction technique. Experimental parameters such as contact time, diluents, effect of H⁺ and Cl^? concentration, and acid durability have been thoroughly investigated. The loading capacity toward Pd(II) was determined to be 113 mg/L using 0.25 mM CADTTCA. The extractant showed high selectivity and extractability for Pd(II) than the other metal ions present in automotive catalyst residue (ACR) solution containing platinum group (PGMs) metal ions (i.e., Pd(II), Pt(IV), Rh(II), La(III), Al(III) and Ce(III)). The recovery percentage of Pd(II) was 98% after five extraction-scrubbing-stripping cycles. The probable extraction mechanisms were established through the FT-IR spectral analysis.     

Cr(VI)-乙酸复合体系中硫酸盐掺杂的含钛高炉渣光催化还原Cr(VI)

采用煅烧的硫酸盐掺杂的含钛高炉渣作光催化剂,研究了Cr(VI)-乙酸(AA)复合体系中Cr(VI)的光催化还原效率,考察了初始pH值、Cr(VI)初始浓度、AA/Cr(VI)体积比、协同效率因子、光催化剂使用寿命等因素的影响. 结果表明,增大AA/Cr(VI)比到0.2%,Cr(VI)的还原效率先增大到27.55%随后逐渐降低. 酸性条件下,Cr(VI)单一体系和Cr(VI)-AA复合体系中Cr(VI)的还原率和吸附率都明显提高;相同反应时间下(110 min),初始pH 1.5时,2种体系中Cr(VI)的还原效率分别为76.32%(单一体系)和100%(复合体系). 复合体系中协同效率因子始终大于0. 循环使用5次后催化剂对Cr(VI)的光催化还原率为92.2%. Cr(VI)在Cr(VI)-AA体系中的光催化还原遵循Langmuir-Hinshelwood动力学规律.     

Preparation of magnetic zeolite/chitosan composite using silane as modifier for adsorption of Cr(VI) from aqueous solutions

This study aimed to prepare an efficient, cost-effective, and separable magnetic zeolite/chitosan composite (MZFA/CS) adsorbent from solid waste to deal with the water pollution of Cr(VI). The MZFA/CS was characterized by X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and vibrating sample magnetometer (VSM) techniques. Then, the effect of pH, temperature, initial concentration of Cr(VI) ions, and contact time was considered in the study. For a sorbent dose of 0.1 g in 50 mL of a Cr(VI) solution, at a contact time of 30 min, temperature of 30°C, and a pH of 3, an adsorption capacity (q_e) of 16.96 mg g⁻¹ was achieved. Adsorption kinetics and isotherm data obtained for all adsorption systems were well-fitted by pseudo-second-order and Langmuir models, respectively. The thermodynamic study suggested that the adsorption process is spontaneous and endothermic in nature. In summary, the adsorbent with better separability (Ms = 16.83 emu g⁻¹) and adsorbability was successfully fabricated.     

Adsorption of Cr (VI) Oxyanions onto Modified Wood Pulp

A new adsorbent was prepared from wood pulp (WP) after reaction with epichlorohydrin and dimethylamine in the presence of pyridine and N,N-dimethylformamide (DMF). The adsorption of Cr (VI) from aqueous solutions by the so-prepared wood pulp adsorbent (WP-A) was investigated. Various factors affecting adsorption, such as pH, adsorbent concentration (1–5 g/L), agitation time (5–60 min), and Cr (VI) concentration (50–700), were taken into consideration. The adsorption of Cr (VI) onto (WP-A) was found to be pH-dependent and maximum adsorption was obtained at pH 3. The adsorption data obeyed Langmuir and Freundlich adsorption isotherms. The Langmuir adsorption capacity (Q_max) was found to be 588.24 mg/g. Freundlich constants, K_F and n, were found to be 55.03 and 2.835, respectively.     

Inhibited Cr(VI) formation in Cr2O3-containing refractory castable using reactive MgO as hydraulic binder

Reactive MgO was used in the first time as alternative hydraulic binder of calcium aluminate cement (CAC) to prepare Cr₂O₃-bearing refractory castable. The formation of Cr(VI), and physical and mechanical properties of MgO-bonded refractory castables after heat-treating were investigated. Microstructural characterization and phase composition analyses on the heat-treated MgO-bonded refractory castable matrices resulted in a comprehensive understanding of the mechanism for the inhibition of Cr(VI), and of the strength development during firing. The results indicate that compared with CAC, Cr(VI) levels were 6.7–28.1 times lower using reactive MgO after firing at 700–1300 °C. The in situ Mg(Cr,Al)₂O₄ spinel formed from the preferential interactions among MgO and Cr₂O₃ and Al₂O₃ would be the main reason leading to the inhibited Cr(VI) formation and strength development during firing.     

Kinetic Study of an Effective Pb(II) Transport through a Bulk Liquid Membrane Containing Calix[6]arene Hexaester Derivative as a Carrier

The article describes transport of Pb(II) through bulk liquid membrane (BLM) containing calix[6]arene hexaester derivative (1) as a carrier. The effect of various parameters such as temperature, carrier concentration, stirring speed and type of solvent on the Pb(II) transport efficiency of the carrier through BLM was evaluated. The activation energy values for the extraction and re-extraction were found as 56.33 kJ mol^?1 and 14.79 kJ mol^?1, respectively. These values demonstrate that the process is diffusionally controlled by Pb(II). Observations indicate that the membrane entrance and exit rate constants (k₁, k₂) increase with increasing stirring speed as well as carrier concentration and decrease with increasing temperature. The effect of solvent on k₁ and k₂ was found to be in the order of CH₂Cl₂ > CHCl₃ > CCl₄.     

A new bioinorganic process for the remediation of Cr(VI)

Palladised biomass of Desulfovibrio desulfuricans ATCC 29577 (bio‐Pd(0)) effected reduction of Cr(VI) to Cr(III) under conditions where biomass alone or chemically‐prepared Pd(0) were ineffective. Reduction of 500 µmol dm^?3 Cr(VI) by 0.4 mg cm^?3 bio‐Pd(0) (Pd : biomass ratio of 1:1) was achieved from 1 mol dm^?3 formate/acetate buffer at pH 1–7 at room temperature; the optimum pH was 3.0. The ratio of mass of Pd : dry mass of biomass, and the need for finely ground bio‐Pd(0) were important parameters for optimal Cr(VI) reduction, with a ratio of 1:1 giving 100% reduction of 500 µmol dm^?3 Cr(VI) within 6 h at room temperature, decreasing to 30 min following heat treatment of the Pd(0)‐loaded biomass. The reduced Cr was recovered quantitatively as soluble Cr(III) at pH 3.0 with no poisoning of the bioinorganic catalyst with respect to continued reduction of Cr(VI). © 2002 Society of Chemical Industry     

Polydopamine dots as an ultrasensitive fluorescent probe switch for Cr(VI) in vitro

Because of the great demand for fluorescent materials, fluorescent dyes, semiconductor quantum dots, and carbon‐based quantum dots have been studied extensively. However, the poor photostability and potential biological toxicity need to be resolved. In this study, we demonstrated the synthesis of a new biomass quantum dot, the polydopamine dot (PDADs), via a simple hydrothermal method under an acidic environment. This new biomass quantum dot showed not only remarkable photoluminescence properties (quantum yield = 0.93) but also a high stability and low toxicity. Moreover, these PDADs could be used as a fluorescent probe for the rapid detection of Cr(VI) (response time = 0.01 s). The detection limit (1 × 10^?11 M ) is the lowest detection limit reported for Cr(VI) fluorescent probes. The mechanism efficient quenching progress could have been due to the fast redox progress between the PDADs and Cr(VI). Moreover, we also showed a practical application of PDADs for Cr(VI) detection in vitro . © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44784.     

Heterocyclic modification of chitosan for the adsorption of Cu (II) and Cr (VI) ions

A heterocyclic modification of chitosan has been attempted for development of an effective adsorbent material for removal of metal ions. The modified polymer was characterized using infrared (IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) techniques. The adsorption capacity exhibited for Cu (II) and Cr (VI) were 83.75 and 85.0 mgg^?1, respectively, which is a significant improvement over chitosan. The adsorption on the modified polymer was a second-order kinetic process and followed Langmuir isotherm model. The thermodynamic analysis indicated exothermic and spontaneous nature of adsorption. About 80% of the adsorbed metal ions were desorbed in appropriate stripping solutions indicating reusability.     

Transport of chromium(VI) through a Cyanex 921‐supported liquid membrane from HCl solutions

The transport of chromium(VI) through a flat‐sheet supported liquid membrane containing Cyanex 921 as a carrier has been investigated. The permeation of the metal is investigated as a function of various experimental variables: hydrodynamic conditions, concentration of chromium(VI) and HCl in the feed phase, carrier concentration and diluent in the membrane and strippant concentration in the stripping phase. The mass transfer coefficient and the thickness of the aqueous boundary layer were calculated from the experimental data. Furthermore, the selectivity of Cyanex 921‐based flat‐sheet supported liquid membrane towards different metal ions and the behaviour of the system against other carriers are presented. Copyright © 2003 Society of Chemical Industry