Fossil fuels have a high energy density, meaning they contain a significant amount of energy per unit of volume, making them efficient for energy production and transport. Biodiesel is especially becoming a fossil fuel alternative and a key part of renewable energy. Several types of waste from homes, markets, street vendors, and other industrial places were collected and transesterified with Ni-doped ZnO nanoparticles for this study. These included castor oil, coffee grounds, eggshells, vegetable oil, fruit peels, and soybean oil. The Ni-doped ZnO’s were then calcined at 800 °C. The maximum conversion rate found in converting fruit peel waste into biodiesel is about 87.6%, and it was 89.6% when the oil-to-methanal ratio was about 1:2 and the reaction time was 140 min. This is the maximum biodiesel production compared to other wastes. Moreover, using vegetable oil with nanocatalyst, the maximum biodiesel production rate of about 90.58% was recorded with 15% catalyst loading, which is the maximum biodiesel production compared with the other wastes with nanocatalyst. Furthermore, at 75 °C and a concentration of catalyst of about 15% the maximum biodiesel production obtained by using castor oil is about 92.8%. It has the highest biodiesel yield compared with the yield recorded from other waste. The catalyst also demonstrated great stability and reusability for the synthesis of biodiesel. Using waste fruit peels with Ni-doped ZnO helps to progress low-cost and ecologically friendly catalyst for sustainable biodiesel production.

Exploring waste-derived catalysts for sustainable biodiesel production: a path towards renewable energy
    Abstract
    1 Introduction
    2 Materials and methods
        2.1 Materials used
        2.2 Synthesis of nanomaterials
    3 Results and discussion
        3.1 Effect of oil: methanal molar ratio
        3.2 Reaction time
        3.3 Concentration of catalyst
        3.4 Effect of temperature
    4 Conclusion
    Acknowledgements 
    References

• T. Sathish(Department of Mechanical Engineering, Saveetha School of Engineering, SIMATS, Chennai, Tamil Nadu, India)
• Sivamani Selvaraju(Department of Chemical Engineering, University of Technology and Applied Sciences, Salalah, Oman)
• N. Ahalya(Department of Biotechnology, MS Ramiah Institute of Technology, Bangalore, Karnataka 560054, India)
• Ashok Kumar(Chitkara Centre for Research and Development, Chitkara University, Chandigarh, Himachal Pradesh 174103, India)
• Abhishek Agarwal(Department of Mechanical and Manufacturing Engineering Technology, Vermont State University, Randolph Center, Vermont, USA)
• Chander Prakash(University Centre for Research and Development, Chandigarh University, Mohali, Punjab 140413, India)
• N. Senthilkumar(Department of Chemistry, Graphic Era (Deemed to Be University), Dehradun, Uttarakhand, India)
• V. Jagadeesha Angadi(Department of Physics, P.C. Jabin Science College, Hubballi 580031, India)
• Vinay Kumar(Bioconversion and Tissue Engineering (BITE) Laboratory, Department of Community Medicine, Saveetha Medical College and Hospital, Saveetha Institute of Medical and Technical Sciences (SIMATS), Chennai, Thandalam 602105, India)
• Abdullah A. Al‑Kahtani(Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, 11451 Riyadh, Saudi Arabia)
• Elham Khalili(Department of Electrical and Engineering, Faculty of Engineering and Physical Science, Centre of Vision Speech, and Processing, University of Surrey, Surrey, UK)
• Hesam Kamyab(Department of Biomaterials, Saveetha Dental College and Hospital, Saveetha Institute of Medical and Technical Sciences, Chennai 600 077, India, Faculty of Architecture and Urbanism, UTE University, Calle Rumipamba S/N and Bourgeois, Quito, Ecuador)
• Mohammad Yusuf(Clean Energy Technologies Research Institute (CETRI), Faculty of Engineering and Applied Science, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada) Corresponding author