Tailoring natural zeolites by acid treatments Yuting Lin*, Alice Lecus**, Joseph Corrao***, Marcia Silva**** *UWM Water Technology Accelerator 247 W. Freshwater Way, 53204 Milwaukee, USA – lin43@uwm.edu ** UWM Water Technology Accelerator 247 W. Freshwater Way, 53204 Milwaukee, USA – ralecus@uwm.edu ***UWM Water Technology Accelerator 247 W. Freshwater Way, 53204 Milwaukee, USA – corrao@uwm.edu **** UWM Water Technology Accelerator 247 W. Freshwater Way, 53204 Milwaukee, USA – msilva@uwm.edu

INTRODUCTION This study focuses on the improvement of adsorption properties of porous materials through cleaning and acid treatment. The material, primarily silica and alumina, has been found to be effective in adsorption of pollutants in water. The adsorption surface area, pore width, and pore volume all play a role in how effectively a material can adsorb other substances onto its pores. This study shows that properties of natural zeolites can be tailored with acid treatment conferring different properties to the porous material, increasing or reducing surface area and pore diameter, depending on the nature of the acid.

MATERIALS & METHODS Figure 1 – Acid treatment reflux process The material went through an initial cleaning process involving sonication, microwaving, and drying at 24 hours in an oven at 100°C. After the cleaning process the material underwent acid treatment. Acid treatments were performeda using concentrated hydrochloric, acetic, nitric, and sulfuric acids. The 20g. of clean zeolite was added to a boiling flask containing 115mL of DI water and 10 mL of acid. Once the zeolite and acid solution were mixed, the flask was refluxed between 80 and 90°C for 12 hours with a vigreux column attached. At the end of 12 hours the treated samples were rinsed with absolute ethanol, followed by further rinsing with DI water. Surface area and pore volume/size analysis was determined with a Quantachrome Autosorb IQ2 gas sorption analyser using Nitrogen adsorptive at 77K. Fourier Transform Infrared (FTIR) spectroscopy was performed utilizing the ATR method on a Shimadzu IR Tracer 100. Raman Spectra was obtained using a Horiba XploRA PLUS raman microscope. DTG data was acquired using a Shimadzu DTG-60 model. MATERIALS & METHODS Figure 1 – Acid treatment reflux process

RESULTS & DISCUSSIONS Table 1 – Sample surface area, pore volume, and pore diameter of natural zeolite that were exposed to different acid treatments. After modification of the porous material, the surface area, pore volume, and pore diameter was examined using gas sorption analysis (Table 1) indicated that the treatment with HCl was by far the best for improvement of surface area.

RESULTS & DISCUSSIONS Figure 2 –Results from gas adsorption analysis. The treatment with HCl was by far the best for improvement of surface area. However, the pore diameter was the smallest (~7Å), Treatment with nitric acid and sulfuric acid conferred great surface area (187Å and 108Å), respectively, while the pore diameter remained similar (~10 Å). Our previous research has shown that surface area is dependent on the breakdown of the zeolite filaments into smaller pieces.

RESULTS & DISCUSSIONS Figure 3 –Results from FTIR analysis. The HCl treated material has the highest intensity absorbance peak for the Si-O-Si band. This treatment was the most effective in increasing the overall Si/Al ratio. the Al-Mg-OH peak was the absolute lowest with the HCl treated sample, further indicating not only the effectiveness of its ability to dealuminate the framework, and once again increasing the overall Si/Al ratio of the material.

RESULTS & DISCUSSIONS Figure 4 –Results from DTG showing the percentage of the mass lost as the treated materials reach 600°C. Nitric acid and HCl treatments having the highest dealumination as water associated with extra-framework cations and aluminium are related to the 100–400°C region (Aytes and Hardacre, 2012). Acetic acid, which is a weak acid, has the least dealumination effect as expected.

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