## 4 Conclusions  
This study has demonstrated the synthesis of OLNCs from the flame pyrolysis of waste cooking oil. This resulted in high-quality carbon nanomaterial composites (TiO\({}_{2}\)/OLNC), where the amount of OLNCs was varied (10 mg, 20 mg, 30 mg, and 50 mg). The nanocomposites were effective in the photocatalytic degradation of MO compared to TiO\({}_{2}\) alone, with the TC-10 material having the faster kinetic rate. This was attributed to synergy between TiO\({}_{2}\) and the OLNCs.  
The addition of H\({}_{2}\)O\({}_{2}\) greatly enhanced the photocatalytic activity of the photocatalyst due to the harvesting of electrons by the H\({}_{2}\)O\({}_{2}\), thus limiting recombination. No formation of chromophoric compounds was detected when the as prepared photocatalysts were applied in the degradation of methyl orange. Overall, the TiO\({}_{2}\)/OLNCs nanocomposites have potential to be applied as photocatalysts for MO degradation. This was achieved by converting a waste material (waste cooking oil) to onion-like nanocarbons, which were added to TiO\({}_{2}\). This allowed for better photocatalytic activity for the nanocomposites than pure TiO\({}_{2}\), due to enhanced adsorption capability. The study has shown that nanocomposites of OLNCs/TiO\({}_{2}\) are potential photocatalysts for the photocatalytic degradation of methyl orange.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13085125/s1](https://www.mdpi.com/article/10.3390/app13085125/s1)]([https://www.mdpi.com/article/10.3390/app13085125/s1](https://www.mdpi.com/article/10.3390/app13085125/s1)), Figure S1: PXRD patterns of anatase TiO\({}_{2}\) phase for TC-10, TC-20, TC-30, and TC-50. Figure S2: XPS survey spectra of TC-10 photocatalyst (a), deconvoluted spectra for Ti (b), C (c) and O (d) respectively. Figure S3: Linear plots for Langmuir isotherm TC-10 (a), TC-20 (b), TC-30 (c), TC-50 (d) and the Fruendlich isotherm TiO\({}_{2}\) (e). Figure S4: Intra-particle diffusion plots for all the catalysts TC-10 (a), TC-20 (b), TC-30 (c), TC-50 (d) and TiO\({}_{2}\) (e). Table S1: Elemental identification and quantification. Table S2: Data from the deconvoluted XPS spectra. Table S3: Adsorption capacity of all the photocatalysts.  
T.D.N.: conceptualization, methodology, writing--original draft, investigation, formal analysis, writing--review and editing, validation. L.L.S.: data curation, formal analysis, investigation. F.D.: data curation, formal analysis, investigation. N.J.C.: supervision, resources, writing--review and editing, validation. E.N.N.: supervision, resources, writing--review and editing, validation. M.S.M.-N.: conceptualization, supervision, resources, project administration, writing--review and editing, validation. All authors have read and agreed to the published version of the manuscript.  
This work was supported in part by the National Research Foundation of South Africa (Grant number: 138075), the University of the Witwatersrand and the DSI-NRF Centre of Excellence in Strong Materials (CoESM). The authors would like to acknowledge [PERSON] (University of Johannesburg, Auckland Park) for the high magnification TEM analysis.  
The study did not require ethical clearance.  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.  
The authors report no conflict of interest.