Abstract
The reuse of waste materials for water treatment purposes is an important approach for promoting the circular economy and achieving effective environmental remediation. This study examined the use of bone char/titanium dioxide nanoparticles (BC/nTiO2) composite and UV for As(III) and As(V) removal from water. The composite was produced via two ways: addition of nTiO2 to bone char during and after pyrolysis. In comparison to the uncoated bone char pyrolyzed at 900 °C (BC900), nTiO2 deposition onto bone char led to a decrease in the specific surface area and pore volume from 69 to 38 m2/g and 0.23 to 0.16 cm3/g, respectively. However, the pore size slightly increased from 14 to 17 nm upon the addition of nTiO2. The composite prepared during pyrolysis (BC/nTiO2)P had better As removal than that prepared after pyrolysis with the aid of ultrasound (BC/nTiO2)US (57.3% vs. 24.8%). The composite (BC/nTiO2)P had higher arsenate oxidation than (BC/nTiO2)US by about 3.5 times. Arsenite oxidation and consequent adsorption with UV power of 4, 8 and 12 W was examined and benchmarked against the composite with visible light and BC alone. The highest UV power was found to be the most effective treatment with adsorption capacity of 281 µg/g followed by BC alone (196 µg/g). This suggests that the effect of surface area and pore volume loss due to nTiO2 deposition can only be compensated by applying a high level of UV power.
Highlights
Elevated arsenic concentration in ground water is a global concern that affects drinking water availability, and food safety [1]
The composite (BC/nTiO2)P proved to be more effective in arsenite removal (57.3% vs. 24.8%) and photocatalytic oxidation (3.5 times higher arsenate produced)
It was found that power levels of 4 and 8 W had a lower As adsorption capacity than that of (BC/nTiO2)P with visible light and BC pyrolyzed at 900 ◦C (BC900)
Summary
Elevated arsenic concentration in ground water is a global concern that affects drinking water availability, and food safety [1]. Arsenite (As(III)) is the most toxic form of inorganic arsenic. It is present as uncharged arsenious acid in the pH range of 6.5–8.5, which makes it less amenable to adsorption compared to arsenate (As(V)) at the same pH range [2,3]. Oxidizing As(III) to As(V) was introduced as a viable way of improving inorganic As removal from water. Recent studies have provided an extensive explanation for the mechanism of oxidizing organic and inorganic As(III) to As(V). The oxidation process may be chemically achieved using ozone or iron and manganese compounds, microbiologically using Herminiimonas arsenicoxydans (known as ULPAs1) [4], or photochemically by applying ultraviolet radiation (UV) with or without activating agents such as TiO2, H2O2 or sulfur [5]
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