Patiparn Punyapalakul

Effects of Surface Functional Groups and Porous Structures on Adsorption and Recovery of Perfluorinated Compounds by Inorganic Porous Silicas

The effects of porous structures and surface functional groups (silanol, 3-aminopropyltriethoxy, 3-mercaptopropyltrimethoxy, n-octyldichloroethoxy, and titanium substitution) on perfluorinated compounds (PFCs) adsorption and recovery were evaluated. The adsorption of PFCs on all adsorbents followed the pseudo-second-order model, and the adsorption rate was controlled by the pore diffusion, except for microporous zeolites and powder activated carbon (PAC). 3-aminopropyltriethoxy-grafted surface produced the highest PFCs adsorption capacities. Perfluorooctane sulfonic acid (PFOS) recovery from silica-based adsorbents (by ethanol extraction) efficiencies were higher than those of PAC and approached 100%. Hydrophobic organic functional groups can protect mesoporous structure from hydrolysis reactions in adsorption and solvent recovery processes. Supplemental materials are available for this article. Go to the publishers online edition of Separation Science & Technology to view the free supplemental file.

Adsorption characteristics of haloacetonitriles on functionalized silica-based porous materials in aqueous solution.

The effect of the surface functional group on the removal and mechanism of dichloroacetonitrile (DCAN) adsorption over silica-based porous materials was evaluated in comparison with powdered activated carbon (PAC). Hexagonal mesoporous silicate (HMS) was synthesized and functionalized by three different types of organosilanes (3-aminopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane and n-octyldimethysilane). Adsorption kinetics and isotherm models were used to determine the adsorption mechanism. The selective adsorption of five haloacetonitriles (HANs) in the single and mixed solute systems was also studied. The experiments revealed that the surface functional groups of the adsorbents largely affected the DCAN adsorption capacities. 3-Mercaptopropyl-grafted HMS had a high DCAN adsorption capacity compared to PAC. The adsorption mechanism is believed to occur via an ion-dipole electrostatic interaction in which water interference is inevitable at low concentrations of DCAN. In addition, the adsorption of DCAN strongly depended on the pH of the solution as this related to the charge density of the adsorbents. The selective adsorption of the five HANs over PAC was not observed, while the molecular structure of different HANs obviously influenced the adsorption capacity and selectivity over 3-mercaptopropyl-grafted HMS.

Effects of crystalline structures and surface functional groups on the adsorption of haloacetic acids by inorganic materials.

The effects of the crystalline structure and surface functional groups of porous inorganic materials on the adsorption of dichloroacetic acid (DCAA) were evaluated by using hexagonal mesoporous silicates (HMS), two surface functional group (3-aminopropyltriethoxy- and 3-mercaptopropyl-) modified HMSs, faujasite Y zeolite and activated alumina as adsorbents, and compared with powdered activated carbon (PAC). Selective adsorption of HAA(5) group was studied by comparing single and multiple-solute solution, including effect of common electrolytes in tap water. Adsorption capacities were significantly affected by the crystalline structure. Hydrogen bonding is suggested to be the most important attractive force. Decreasing the pH lower than the pH(zpc) increased the DCAA adsorption capacities of these adsorbents due to electrostatic interaction and hydrogen bonding caused by protonation of the hydronium ion. Adsorption capacities of HAA(5) on HMS did not relate to molecular structure of HAA(5). Common electrolytes did not affect the adsorption capacities and selectivity of HMS for HAA5, while they affected those of PAC.

Selective adsorption mechanisms of antilipidemic and non-steroidal anti-inflammatory drug residues on functionalized silica-based porous materials in a mixed solute

The selective adsorption mechanisms of naproxen (NAP), acetaminophen (ACT), and clofibric acid (CFA) on silica-based porous materials were examined by single and mixed-batch adsorption. Effects of the types and densities of surface functional groups on adsorption capacities were determined, including the role of hydrophobic and hydrophilic dissolved organic matters (DOMs). Hexagonal mesoporous silica (HMS), superparamagnetic HMS (HMS-SP) and SBA-15 were functionalized and applied as adsorbents. Compared with powdered activated carbon (PAC), amine-functionalized HMS had a better adsorption capacity for CFA, but PAC possessed a higher adsorption capacity for the other pharmaceuticals than HMS and its two derivatives. In contrast to PAC, the adsorption capacity of the mesoporous silicas varied with the solution pH, being highest at pH 5. Electrostatic interactions and hydrogen bonding were found to be the main mechanisms. Increase in grafted amine group density on silica surfaces can enhance the CFA adsorption capacity. Further, hydrophilic DOM can decrease CFA adsorption capacities on amino-grafted adsorbents by adsorption site competition, while hydrophobic DOM can interfere with CFA adsorption by the interaction between hydrophobic DOM and CFA. Finally, in a competitive adsorption study, the adsorption capacity of hydrophilic adsorbents for acidic pharmaceuticals varied with their pKa values.

Adsorption of ciprofloxacin on surface functionalized superparamagnetic porous silicas

AbstractThe effect of surface functional groups 3-aminopropyltriethoxy- and 4-(triethoxysilyl)-butyronitrile-, 3-mercaptopropyltriethoxy-, phenyltrimethoxy-, and n-octyl-dimethoxychloro- grafted superparamagnetic particles coated with hexagonal mesoporous silicas (HMS-SPs) on the adsorption of ciprofloxacin (CIP) was evaluated. CIP adsorption followed the pseudo-second-order kinetic model, and intraparticle diffusion was suggested to be the rate-controlling step. Higher CIP adsorption capacities revealed on the hydrophobicity of the adsorbents, however, the phenyltrimethoxy group had the highest adsorption capacity due to the interaction of electron-donor acceptors. The adsorption capacities strongly depended on an electrostatic interaction, with the exception of the phenytrimethoxy group. The presence of tannic acid (TA) could increase the adsorption capacity of CIP on adsorbent surfaces by multilayer adsorption between a positively charged amine group of CIP and negatively charged TA.

Removal of haloacetonitriles in aqueous solution through adsolubilization process by polymerizable surfactant-modified mesoporous silica

To investigate the adsorption properties and mechanisms of haloacetonitriles (HANs), large-pore SBA-15 mesoporous silica (SBA-CHX) was synthesized using cyclohexane as a swelling agent, and the surface was modified with polymerizable gemini surfactant (PG). The structure and textural properties of the synthesized adsorbents were characterized. PG surfactant coverage on the surface and the degree of polymerization were confirmed with FT-IR analysis. Adsorption experiments were performed under batch conditions to evaluate the influence of the contact time, adsorption isotherms, the effect of the pH solution, and the selective adsorption of five haloacetonitriles (HAN(5)) in individual-solute and mixed-solute solutions and surfactant leaching studies. The results indicated that the hydrophobic HANs were efficiently adsorbed onto PG surfactant-modified SBA-CHX. The selective adsorption mechanisms involved a more complex interplay between the organic partition, surface adsorption (i.e., ion-dipole electrostatic interactions) and hydrophobic interaction that depended upon the adsorbent and adsorbate characteristics. An increased degree of halogen substitution in the HAN molecule significantly affected the adsorption capacity and selectivity by the organic partition. Polymerization of the polymerizable surfactant increased the stability of the adsorbed surfactant on the adsorbent surface.

Photodegradation of haloacetonitriles in water by vacuum ultraviolet irradiation: Mechanisms and intermediate formation

Photodegradation of haloacetonitriles (HANs), highly carcinogenic nitrogenous disinfection by-products, in water using vacuum ultraviolet (VUV, 185xa0+xa0254xa0nm) in comparison with ultraviolet (UV, only 254xa0nm) was investigated. Monochloroacetonitrile (MCAN), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), and dibromoacetonitrile (DBAN) were species of HANs studied. The effect of gas purging and intermediate formation under VUV were examined. The results show that the pseudo first order rate constants for the reduction of HANs under VUV were approximately 2-7 times better than UV. The order of degradation efficiency under VUV and UV was MCANxa0<xa0DCANxa0<xa0TCANxa0<xa0DBAN. The degradation efficiencies of individual HANs under VUV were higher than those of mixed HANs, suggesting competitive effects among HANs. Under nitrogen purging, the removal rate constants of mixed HANs was much higher than that of the aerated condition by 34.4, 34.9, 10.1, and 3.8 times for MCAN, DCAN, TCAN, and DBAN, respectively. The major degradation mechanism for HANs was different depending on HANs species. Degradation intermediates of HANs such as 2-chloropropionitrile, 2,2-dimethylpropanenitrile, and fumaronitrile were produced from the substitution, addition, and polymerization reactions. In addition, chlorinated HANs with lower number of chlorine atom including MCAN and DCAN were found as intermediates of DCAN and TCAN degradation, respectively.

Adsorption of single and mixed haloacetonitriles on silica-based porous materials: Mechanisms and effects of porous structures

Adsorption mechanisms and the role of different porous and crystalline structures on the removal of five haloacetonitriles (HANs) over hexagonal mesoporous silica (HMS), titanium substituted mesoporous silica (Ti-HMS), rod-shaped SBA-15 and microporous zeolite NaY were investigated. In addition, the effect of pH on adsorption mechanism and selective adsorption of five HANs individually and in an equimolar mixed solution were evaluated. The results indicated that the intraparticle diffusion rate constants of the mesoporous adsorbents were higher than that of the microporous NaY. In single solute, the order of adsorption preference (highest to lowest) was mono-HANsu202f>u202fdi-HANsu202f>u202ftri-HAN. However, in mixed solute, the large molecular weight of the tri-HAN and di-HANs are more easily adsorbed than the smaller molecular weight mono-HANs. Except for SBA-15, the order of adsorption capacities in mixed HANs solute was not different compared to that observed for the single HAN solute, which might be caused by the higher accessibility to the active sites due to larger pore size. The ion-dipole electrostatic interaction was likely to be the main adsorption mechanism, and was favored at high pH values due to the high negative surface charge density of the adsorbent. The molecular structure of the HANs and hydrophilic/hydrophobic nature affected the adsorption capacities and their selective adsorption from mixed solutes.