Laser-Induced Biochar Formation through 355 nm Pulsed Laser Irradiation of Wood, and Application to Eco-Friendly pH Sensors

Due to the limited availability of agricultural land, pH sensing is becoming more and more important these days to produce efficient agricultural products. Therefore, to fabricate eco-friendly and disposable sensors, the black carbon, which is called biochar, is formed by irradiation of a UV pulsed laser having a wavelength of 355 nm onto wood and applying the resulting material as a pH sensor. The surfaces of three types of wood (beech, cork oak, and ash) were converted to the graphitic structure after UV laser irradiation; their morphologies were investigated. In addition, since the content of lignin, an organic polymer, is different for each wood, optimal laser irradiation conditions (laser fluence) needed to form these woods into pH sensors were considered. Depending on the degree of oil-like material generated after laser irradiation, a disposable pH sensor that can be used from one to three times is fabricated; due to the environmental characteristics of wood and biochar, the sensor shows high availability in that it can be easily discarded after use on agricultural land. After that, it can be used as filter in soil. Our wood-based pH sensor sensitively measures sequential changes from pH 4 to pH 10 and shows a very linear change of △R/R, indicating its potential for use in agriculture.