First Advisor

Jie Lin

Term of Graduation

Winter 2000

Date of Publication

2-3-2000

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Chemistry

Department

Chemistry

Language

English

Subjects

Extraction (Chemistry), Optical detectors, Hydrogen-ion concentration -- Measurement, Sorbents, Sewage -- Purification -- Heavy metals removal

Physical Description

1 online resource (2, x, 107 pages)

Abstract

Sol-gel silica is a porous glasslike material that can be prepared at room temperature. In this work, sol-gel method was employed to develop sol-gel sensors for pH measurement and sol-gel silica sorbents for removal of heavy metals.

Sol-gel pH sensors were prepared by entrapping pH indicators in porous solgel silica films. The feasibility of developing optical pH sensors with linear response over a wide pH range by using mixtures of multiple indicators was demonstrated. Theoretical criteria and experimental procedures for selecting indicators and determining optimum ratios of indicators were discussed. A linear response over 4.5 pH units was obtained for a mixture of four indicators in solution. A sol-gel silica pH sensor with a linear response over 3.4 pH units was developed by co-entrapping three indicators. In both cases, a standard deviation of pH equal to 0.03 was obtained. It was found that the entrapment of pH indicators in sol-gel silica caused shifts in the spectra and pKa of indicators. Such phenomena were studied and interpreted by the interaction between the indicator and charged silica surface, interaction between the indicator and surfactant micelles, and the spatial constraint of silica pore. Ionic strength has a much larger effect on the pKa of pH indicators entrapped in sol-gel silica than in solution. The response time of sol-gel pH sensor is less than 5 minutes and its half-life can be as long as 630 days.

Sol-gel silica sorbents for the removal of heavy metals were developed by entrapping three organic dyes, cibacron blue, cibacron red and direct yellow, in sol-gel silica particles. Removal characteristics of Zn(II), Cd(II) and Pb(II) from aqueous solutions by the sorbents were studied, including removal kinetics, pH effect, removal isotherm and modeling, nature of the removal, regeneration and reuse of the sorbents. The sorbents showed removal capacity of 4.72 mg Zn, 5.74 mg Cd, and 13.9 mg Pb per gram sorbent, respectively. Used sol-gel silica sorbents can be regenerated with 1M HCl or 1M NaCl and recycled for at least 3 times without significant decrease in removal capacity.

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Persistent Identifier

https://archives.pdx.edu/ds/psu/44689

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