Fabrication of novel agrowaste (banana and potato peels)-based biochar/TiO2 nanocomposite for adsorption of Cr(VI), statistical optimization via RSM approach by Ashfaq, Aamna, Nadeem, Raziya, Gong, Hongyu, Rashid, Umer, Saima Noreen, Rehman, Shafique ur, Ahmed, Zubair, Adil, Muhammad, Akhtar, Nayab, Ashfaq, Muhammad Zeeshan, Alharthi, Fahad A., Kazerooni, Elham Ahmed