Enhanced adsorption of fluoride on Al-modified boron nitride nanosheets from aqueous solution

Though fluoride is a necessity for human body, excessive intake probably leads to irreversible damages such as dental fluorosis, skeletal fluorosis and lesions of the endocrine glands, thyroid and liver. Herein boron nitride nanosheets (BNNSs) and a series of Al-modified BNNSs (BNNSs-Al-X) with different Al amounts were first prepared to remove superfluous fluoride in aqueous solution. The modified Al was proved to be amorphous Al2O3 on the surface of BNNSs. Batch adsorption results show that both BNNSs and BNNSs-Al-2, which fits pseudo-second-order model well, have high adsorption rate for fluoride. The maximum adsorption capacity calculated by Langmuir model is 50.510 mg/g for BNNSs-Al-2, which is better than vast majority of reported adsorbents. The excellent adsorption capacity of BNNSs-Al-2 could be attributed to the synergy of porous BNNSs and amorphous Al2O3. Primary BNNSs can adsorb fluoride mainly by physical interaction, while chemical adsorption is predominant on the Al-modified BNNSs, which can be deduced from the fitted model and corresponding parameters. All of the above results prove that BNNSs-Al-2, as a promising adsorbent, can play an important role for removal of fluoride in water.