Supporting Information Green synthesis of carbon quantum dots from lemon peel waste: Applications in sensing and photocatalysis Ankit Tyagi, aǁ Kumud Malika Tripathi, aǁ Narendra Singh, a,b Shashank Choudhary, a and Raju Kumar Gupta *a,b a Department of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur- 208016, UP, India b Center for Nanosciences and Center for Environmental Science and Engineering, Indian Institute of Technology Kanpur, Kanpur-208016, UP, India * Corresponding author. Tel: +91-5122596972; Fax: +91-5122590104. E-mail address: guptark@iitk.ac.in ǁ Contributed equally. Characterization techniques Fourier transform infrared (FTIR) spectra of the wsCQDs were analyzed with Bruker Fourier transform infrared spectrometer (Vector 22 model) using KBr pellets. Zeta potential measurement was done in aqueous solution with Malvern Zetasizer Nano ZS 90 to measure the surface charge on wsCQDs. Thermogravimetric analysis (TGA) was carried out by using a C. I. electronics analyzer on a SDTQ600, TA instruments, (waters LLC, 159 Lukens Drive, New Castle DE 19720) in nitrogen atmosphere at heating rate of 10 ˚C-min -1 and amount of wsCQDs loading over TiO 2 nanofibers was found using TGA. The surface morphology of the wsCQDs and TiO 2 -wsCQDs composites was done by using field-emission scanning electron microscopy (FESEM) SUPRA 40VP, Carl Zeiss (NTS GmbH, Oberkochen, Germany) microscope operated at 10 kV in high vacuum mode and by using transmission electron microscopy (TEM) (Tecnai 20 G2 STWIN model) at an accelerating voltage of 200 kV. Samples for TEM characterization were prepared by drop casting 5µL aqueous solution onto a carbon coated copper grid (mesh size 400) and vacuum dried. UV−visible absorption spectra were performed by Double beam UV-visible spectrometer (Varian Cary 100, Electronic Supplementary Material (ESI) for RSC Advances. This journal is © The Royal Society of Chemistry 2016