Physics and Chemistry of Minerals

Physics and Chemistry of Minerals

Supplementary Information

Studies on the solid acidity of heated and cation-exchanged montmorillonite usingn-butylamine titration in non-aqueous systemand diffuse reflectance Fourier transform infrared spectroscopy(DRIFT)

Hongmei LIU · Dong LIU · Peng YUAN · Daoyong TAN · Jingong CAI · Hongping HE · Jianxi ZHU · Zhiguang SONG

H. Liu · D. Liu · P. Yuan()· D. Tan · H. He · J. Zhu

CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China

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H. Liu · D. Tan

University of Chinese Academy of Sciences, Beijing 100049, China

J. Cai

School of Ocean and Earth Science, Tongji University, Shanghai 200092, China.

Z. Song

The State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.

Determination of the CEC value of montmorillonite

The cobalt hexamine chloride cation (Co(NH3)63+) exchange method was used in our work to measure the value of cation exchange capacity (CEC) of montmorillonite (Mt). The cobalt hexamine chloride was purchased from Aldrich (98%) and used without further purification.

Three parallel tests were conducted for the accuracy. 1 g dry weight Mt was placed in 50 ml polypropylene tubes and 20 ml of0.025mol/L cobalthexamine chloride solution were added.After continuous shaking for 24 hours on a rotating device, tubes were centrifuged at7000 rpm for 10 min.The CEC value was evaluated by comparing the content of the cobalt cations (Co3+) in the solution before and after theexchange of Mt with Co(NH3)63+, using the following equation.

CEC value (mmol/100 g) =3×C×V/M×100

Where C (mmol/L) is the Co3+ concentration obtained by using a UV–Visspectroscopy atwavelength of 472 nm; V (L) is the solution volume; and M (g) is the mass of Mt.

Solid acidity measurement

Hammett indicators were used to estimate the solid acid amount and strength of Mt and its modified products based on the reversible reaction

(1)

K is the equilibrium constant.

The solid acid strength (H0) was obtained by the following equilibrium equation using different Hammett indicators (Table S1):

(2)

When [B] = [BH+], the Hammett indicators began to change the color and H0 = pK. As a result, the solid acid strength was represented by the different pK of various Hammett indicators. The total solid acid amount was the value determined by using the indicator with the largest pK.

The n-butylamine titration using Hammett indicators was performed following the classic procedure. Approximately 0.10 g of montmorillonite powder was dispersed in 2 mL of dry petroleum ether in a series of capped glass bottles, and n-butylamine was then added into each glass bottle from a syringe. The amount of n-butylamine added (N, mmol/g montmorillonite) was range from zero to a value higher than the expected titration amount (mmol n-butylamine per gram of montmorillonite, e.g., if a sample has an anticipated titration amount of 0.10 mmol/g, the amount of n-butylamine added should be 0, 0.10, and 0.20 mmol/g, respectively). In addition, the corresponding volume (V, mL) of n-butylamine added to each glass bottle was calculated using the equation V=NM/C, where: M was the sample mass (~0.10 g) and C was the concentration of n-butylamine (mmol/mL).

The mixture was then ultrasonically shaken for 30 min to achieve adsorption equilibrium. The suspensionin each glass bottle was then distributed into several testtubes, and the different indicators were added. The color-change of the Hammett indicators (Table S1) in each testtube corresponded to complete neutralization. Accordingly, the amountof n-butylamine required was obtained, which was equal to the acid amount.The acid strength (H0) was estimated using Table S1; for example, a sample gave a red coloration with Methyl Red but a yellow coloration with Phynelazona-Phthylamine was estimated to have a acid strength of3.3 H04.8.

Table S1.Hammett indicators used for the determination of the surface acidity of solids

Table S2. Positions and assignments of the DRIFT vibrational bands

1