Optimization of hydrogen storage capacity in silica-supported low valent Ti systems exploiting Kubas binding of hydrogen

Silica-based materials grafted with low valent Ti fragments for Kubas-type binding of hydrogen were optimized for hydrogen adsorption capacity by varying the surface area, pore size, loading levels, and type of organometallic precursor. All materials were characterized by XRD, nitrogen adsorption, and XPS where appropriate. The surface area of HMS silica was optimized by varying silica-to-surfactant molar ratio, and also by tuning the pore size by varying the surfactant’s carbon chain length (C₆, C₈, C₁₀, C₁₂). Then Ti fragments originating from either benzyl, allyl, or methyl Ti precursors were grafted onto the optimal HMS surface at different loading levels to arrive at Ti grafted HMS materials with H₂ storage capacities and binding properties superior to those previously reported by our group for benzyl Ti (III) species on silica. HMS prepared with dodecylamine using a silica:surfactant ratio of 3:1 and subsequently grafted with 0.2 M equiv. of TiBz₄ had the highest H₂ adsorption at 2.45 wt% at 77 k and 60 atm, which equates to an average of 3.98 H₂ molecule per Ti metal center, just one H₂ molecule short of the theoretical saturation limit of 5 H₂/Ti predicted by the 18-electron rule. The H₂ adsorption capacities of Me₃Ti-HMS and Allyl₃Ti-HMS prepared using the same optimized sample of C₁₂-HMS silica at a 3:1 Si:surfactant ratio possessed H₂ adsorption values corresponding to 2.4 and 2.27 H₂ per Ti center, respectively, at 60 atm and 77 K. This performance level is significantly lower than that of the benzyl Ti (III) system. The binding enthalpies of the benzyl Ti (III) material increase with H₂ coverage to 23 kJ/mol, while the enthalpies for the newly synthesized Me₃Ti-HMS and Allyl₃Ti-HMS materials increase with H₂ coverage to a maximum of 2.66 and 4.17 kJ/mol, respectively. XPS studies on these materials suggested a trend in π-back donating ability on the Ti (III) centers of methyl > allyl > benzyl, opposite that observed experimentally. The reason for the diminished performance of the allyl and methyl Ti (III) systems may thus be related to the presence of THF ligands blocking coordination sites in the allyl and methyl systems. THF is not present in the benzyl system because this solvent is not required for synthesis.     

Grafting of organosilane derived from 3-glycidoxypropyltrimethoxysilane and thiourea onto magnesium phyllosilicate by sol–gel process and investigation of metal adsorption properties

A layered inorganic–organic magnesium silicate (Mg-GTPS-TU) has been successfully synthesized by using sol–gel based precursor under mild temperature conditions and a new silylaing agent (GTPS-TU) derived from 3-glycidoxypropyltrimethoxysilane (GTPS) and thiourea (TU) as the silicon source. The hybrid material was characterized through elemental analysis, infrared spectroscopy, X-ray diffractometry, thermogravimetry, and carbon and silicon solid-state nuclear magnetic resonance spectroscopy. The result confirmed the attachment of organic functionality to the inorganic silicon network. The inter-lamellar distance for the hybrid material was found to be 18.8 Å. Metal adsorption characteristics follows Cr(III) >Mn(II)>Zn(II) with more affinity towards Cr(III) in dilute aqueous solution. Evaluation of thermodynamic parameters ΔH and ΔS for Cr(III) were found to be 25.44 J mol⁻¹ and 79.9 J mol⁻¹ K⁻¹, respectively, indicating adsorption process to be endothermic in nature. The negative value of ΔG indicated the feasibility and spontaneity of ongoing adsorption process at relatively higher temperature. The presence of multiple coordination sites in the attached organic functionality expresses the potentiality of the hybrid material containing new silylating agent for heavy cation removal from eco-system.     

Adsorption of Benzene and Propylene in Zeolite ZSM-5： Grand Canonical Monte Carlo Simulations

The adsorption behavior of benzene and propylene in zeolite ZSM-5 was studied by Grand Canonical Monte Carlo(GCMC) simulations. It could be found that benzene and propylene molecules showed different adsorption behavior in the zeolite cavities. The loadings of propylene were significantly larger than those of benzene at 100 kPa. From the figures of potential energy distribution,the potential energy of benzene/zeolite was more negative than that of propylene/zeolite,so benzene could be adsorbed more stably t...     

Modified cellulose fibres for adsorption of dissolved organic solutes

Cellulose fibres were grafted with aliphatic anhydrides having C6, C8, C12 and C16 chain length using a heterogeneous solvent exchange acylation procedure. The ensuing materials were fully characterised by FTIR, solid state ¹³C-NMR, Wide-angle X-ray scattering and contact angle measurements. These techniques showed that the chemical coupling has indeed occurred. The prepared modified fibres appeared to be efficient to trap different organic molecules dissolved in water. Recycling tests revealed that the saturated substrates could be regenerated tens of times without loosing their capacity of absorption of organic contaminants.     

Adsorption at the air-water interface and emulsification properties of grain legume protein derivatives from pea and broad bean

Functional properties of native and modified (through induced autolysis) pea (Pisum sativum L.) and broad bean (Vicia faba L.) protein derivatives are studied. In specific, protein solubility and behavior at the air–water interface through surface pressure measurements are investigated. Furthermore the ability of the protein products to act as emulsifying agents and to stabilize emulsions is studied through oil droplet size distribution measurements and by the protein adsorbed at the oil–water interface. The data reveal that the ability of the proteins to act as surfactants and build up a rigid film around the oil droplets, mainly depends on their suitable molecular configuration and structure. Hydrolysis did not promote the functionality of the legume proteins. Broad bean exhibited better functionality than pea, before and after hydrolysis. Some comparisons were also made with lupin (Lupinus albus L.) protein isolate.     

Kinetics and thermodynamics of bromophenol blue adsorption by a mesoporous hybrid gel derived from tetraethoxysilane and bis(trimethoxysilyl)hexane

A mesoporous hybrid gel is prepared with tetraethoxysilane (TEOS) and bis(trimethoxysilyl)hexane (TSH) as precursors without using any templating agent. Nitrogen sorption, TG-DTA, FTIR, and point of zero charge (PZC) measurement are used to characterize the gel. The gel has a specific surface area of 695 m(2) g(-1) with a pore size of 3.5 nm, a pore volume of 0.564 cm(3) g(-1), and a point of zero charge (PZC) of 6.2. The kinetics and thermodynamics of bromophenol blue (BPB) adsorption by the gel in aqueous solution are investigated comprehensively. The effects of initial BPB concentration, pH, ionic strength, and temperature on the adsorption are investigated. Kinetic studies show that the kinetic data are well described by the pseudo-second-order kinetic model. Initial adsorption rate increases with the increase in initial BPB concentration and temperature. Adsorption activation energy is found to be 62.5-67.5 kJ mol(-1) depending on the initial BPB concentration. Internal diffusion appears to be the rate-limiting step for the adsorption process. The equilibrium adsorption amount increases with the increase in the initial BPB concentration, solution acidity, and ionic strength, but decreases with the increase in temperature. The thermodynamic analysis indicates that the adsorption is spontaneous and exothermic. The adsorption isotherms can be well described with Freundlich equation indicating the heterogeneity of the hybrid gel surface. Electrostatic and hydrophobic interactions are suggested to be the dominant mechanism for adsorption.     

Effects of heavy metals and oxalate on the zeta potential of magnetite

Zeta potential is a function of surface coverage by charged species at a given pH, and it is theoretically determined by the activity of the species in solution. The zeta potentials of particles occurring in soils, such as clay and iron oxide minerals, directly affect the efficiency of the electrokinetic soil remediation. In this study, zeta potential of natural magnetite was studied by conducting electrophoretic mobility measurements in single and binary solution systems. It was shown that adsorption of charged species of Co(2+), Ni(2+), Cu(2+), Zn(2+), Pb(2+), and Cd(2+) and precipitation of their hydroxides at the mineral surface are dominant processes in the charging of the surface in high alkaline suspensions. Taking Pb(2+) as an example, three different mechanisms were proposed for its effect on the surface charge: if pH<5, competitive adsorption with H(3)O(+); if 56, precipitation of heavy metal hydroxides prevails. Oxalate anion changed the associated surface charge by neutralizing surface positive charges by complexing with iron at the surface, and ultimately reversed the surface to a negative zeta potential. Therefore the adsorption ability of heavy metal ions ultimately changed in the presence of oxalate ion. The changes in the zeta potentials of the magnetite suspensions with solution pH before and after adsorption were utilized to estimate the adsorption ability of heavy metal ions. The mechanisms for heavy metals and oxalate adsorption on magnetite were discussed in the view of the experimental results and published data.     

Removal of phenol from aqueous phase by using neutralized red mud

The objective of this study is to remove the phenol from aqueous solution by using the neutralized red mud in batch adsorption technique. The study was carried out as functions of contact time, pH, initial phenol concentration, red mud dosage and effect of salt addition. The experiments demonstrated that maximum phenol removal was obtained in a wide pH range of 1-9 and it takes 10 h to attain equilibrium. The adsorption data was analyzed using the Langmuir and the Freundlich isotherm models and it was found that the Freundlich isotherm model represented the measured sorption data well. The influence of addition of salt on phenol removal depends on the relative affinity of the anions for the red mud surface and the relative concentrations of the anions.     

Solvothermal synthesis and removal capacity for hydrogen chloride gas of Zn(OH)(NO3) with a rare (10,3)-d net

A basic zinc nitrate, [Zn(OH)(NO₃)]_n with a novel framework reported herein is prepared by solvothermal synthesis, and holds a rare three-dimensional (10,3)-d net called by Wells. It crystallizes in orthorhombic, space group, Pna2₁ (No. 33), , , , Z=4, , , , 3.49<θ<27.51, , R₁=0.029, wR₂=0.0773 for 697 (I>2σ(I)) of 1728 [R_(int)=0.0246] unique reflections and 59 parameters. GOF=1.073. Interestingly this basic zinc nitrate, [Zn(OH)(NO₃)]_n behaves well at removal capacity for hydrogen chloride gas, 20.3 g HCl/100 g, and its framework is not destroyed yet. This adsorption character may be useful for the removal of toxic gases in the environment.     

Investigation of ionene adsorption on quartz surfaces by thermal-lens spectrometry

Thermal-lens spectrometry was used for the investigation of the adsorption of ionene to quartz surfaces. The thermooptical analysis of the surface makes it possible to distinguish the modified surface from a clean quartz surface and to provide sensitive direct concentration measurements of the light absorbing co-adsorbed substance. The co-adsorption of chromate ions and 2,10-ionene from aqueous solutions to quartz surfaces was investigated and the desorption procedure proposed.