Effects of Oxygen Partial Pressure on Wood-Based Activated Carbon Treated with Vacuum Ultraviolet Light

Nana Takahashi,Shuichi Shoji,Jun Mizuno,Masahiro Kawamura,Ami Tezuka,Hiroyuki Kuwae,Seren Maeda

doi:10.3390/coatings11040411

Abstract

This study uses vacuum ultraviolet (VUV) light with a wavelength of 172 nm as a surface treatment to enhance the adsorption capacity of wood-based activated carbon (AC). The AC surface treatment is performed under three O2 partial pressure conditions—5.0 × 104 Pa, where ozone (O3) effects dominate; 6.3 × 10−6 Pa, where VUV effects dominate; and 1.9 × 103 Pa for a balanced condition. For the O3-dominant condition, only graphene edge defects are etched (no aromatic carbon bonds are etched), resulting in increased surface roughness. When the VUV effects dominate, aromatic carbon bonds are cleaved, which then reacted with O2 or water adsorbed inside the pores. This increased both the number and size of the mesopores. Under the balanced conditions, the water adsorption capacity was enhanced by 45.5%, which is higher than that obtained before VUV exposure or with VUV under other conditions. This is because the surface roughness increased, as well as the pore sizes and numbers under the balanced condition. These results indicate that we can control VUV-based AC surface treatments via O2 partial pressure.

Highlights

Accepted: 30 March 2021Activated carbon (AC) has high surface areas and adsorption capacities because of oxygen functional groups on the surfaces of micro- and mesoporous structures [1,2]
XPS analysis was conducted with respect to oxygen content and functional groups to examine the chemical effects on the film of woody carbon material (FWCM) from the Vacuum ultraviolet (VUV) treatments
We studied O effects on the VUV treatment of activated carbon (AC) by using three different O partial We studied O22 effects on the VUV treatment of AC by using three different O22 partial pressures that changed the generated O3 /VUV light ratio

Summary

Introduction

Accepted: 30 March 2021Activated carbon (AC) has high surface areas and adsorption capacities because of oxygen functional groups on the surfaces of micro- and mesoporous structures [1,2]. The AC structure derives from the nature of the precursor materials, which could be chemical products (coal, polymers), or natural products (palm shells, crops, wood) [9,10]. Natural-material-based AC is renewable, abundant, and has natural pores [11]. It requires a binder to form shapes, which can degrade the properties by filling the pores and degrade the electrical conductivity [6]. We developed a thin binder-less wood-based AC, a film of woody carbon material (FWCM), that has natural pore structures. It originated from Picea jezoensis (Jezo Spruce) and had an electrical conductivity of 3 × 10−2 S/m [8]. Surface treatment to improve adsorption characteristics is required for wood-based AC

Methods

Results

Conclusion