Unravelling How pH Sequence Shapes Green-Synthesized TiO2 Nanoparticles for Dye-Sensitized Solar Cells

In this study, the influence of pH adjustment sequence during green synthesis on the structural evolution of TiO₂ nanoparticles was investigated, specifically examining whether the solution pH was modified before or after the addition of titanium(IV) isopropoxide (TTIP). Jatropha multifida leaf extract was employed as a natural reducing, capping, and stabilizing agent owing to its rich bioactive compounds, which are capable of directing nanoparticle formation. Two synthesis pathways were systematically compared: pre-pH adjustment, where the extract pH (~5) was adjusted to acidic or basic conditions prior to TTIP addition, and post-pH adjustment, where TTIP was first introduced into the extract, followed by pH modification. The pH values were varied at 3, 7, and 10. The results revealed that the crystallite size increased with increasing pH, and for the same pH value, the post-pH adjustment route consistently produced larger crystallites than the pre-pH adjustment route. Following synthesis, all as-prepared samples were utilized as photoanodes in DSSCs, and their photovoltaic performance was evaluated via current–voltage (I–V) measurements under simulated solar illumination. The pre-pH 3 sample achieved the highest PCE of 5.52%, attributed to its smaller crystallite size, which provides a higher surface area, greater dye loading, and improved charge transport. Thus, the pre-pH adjustment method is more suitable for producing TiO₂ for DSSC applications. This study demonstrates that the timing of pH adjustment controls TiO₂ nucleation and growth, shaping its final structure, and affecting DSSC performance. It provides a simple, green, and scalable way to tune TiO₂ for improved solar cell efficiency.

Dye-sensitized solar cells (DSSCs); Green synthesis; Morphology; pH sequence control; TiO2 nanoparticle

Aftab, S., Khan, N., Amina, M., Liaqat, I., Alkahtani, S., & Mehdi, M. (2025). Advancements in nanomaterials for solar energy harvesting: Challenges, innovations, and future prospects. Chemical Engineering Journal. https://doi.org/10.1016/j.cej.2025.164224

Ahmed, S. F., Mofijur, M., Parthasarathy, P., Rahman, S. M. A., Ong, H. C., Alazwari, M., & Ali, M. A. (2022). Green approaches in synthesising nanomaterials for environmental nanobioremediation: Technological advancements, applications, benefits and challenges. Environmental Research, 204, 111967. https://doi.org/10.1016/j.envres.2021.111967

Ashrafuzzaman, M., Rahman, M. M., Saidur, R., & Long, B. D. (2025). A review of photoanode materials, challenges, and outlook of dye-sensitized solar cells. Journal of Power Sources. https://doi.org/10.1016/j.jpowsour.2025.236636

Behzad, F., Habibi-Yangjeh, A., Vadivel, S., & Dutta, K. (2021). An overview of the plant-mediated green synthesis of noble metal nanoparticles for antibacterial applications. Journal of Industrial and Engineering Chemistry, 94, 92–104. https://doi.org/10.1016/j.jiec.2020.12.005

Chen, H. S., & Kumar, R. V. (2012). Sol–gel TiO? in self-organization process: Growth, ripening and sintering. RSC Advances, 2(6), 2294–2301. https://doi.org/10.1039/C2RA00782G

Dah-Nouvlessounon, D., Adoukonou-Sagbadja, H., Baba-Moussa, F., Sina, H., Ahouansou, R., & Baba-Moussa, L. (2023). Polyphenol analysis via LC–MS–ESI and potent antioxidant, anti-inflammatory, and antimicrobial activities of Jatropha multifida L. extracts used in Benin pharmacopoeia. Life, 13(9), 1898. https://doi.org/10.3390/life13091898

Devadiga, D., Selvakumar, M., Hegde, G., & Bhat, D. K. (2021). Dye-sensitized solar cell for indoor applications: A mini-review. Journal of Electronic Materials, 3187–3206. https://doi.org/10.1007/s11664-021-08854-3

Fan, K., Yu, J., & Ho, W. (2017). Improving photoanodes to obtain highly efficient dye-sensitized solar cells: A brief review. Materials Horizons, 4(3), 319–344. https://doi.org/10.1039/C6MH00511J

Gnanasangeetha, D., & Suresh, M. (2020). A review on green synthesis of metal and metal oxide nanoparticles. Nature Environment and Pollution Technology, 19(5), 1789–1800. https://doi.org/10.46488/NEPT.2020.v19i05.002

Golthi, V., Harikrishna, K., Natarajan, S., Rao, K., Reddy, M. G., & Madhavi, V. (2024). Green synthesis of CuO nanorods using Jatropha podagrica leaf extract for dye degradation and antibacterial applications. Nanotechnology for Environmental Engineering, 9(3), 375–388. https://doi.org/10.1007/s41204-024-00372-x

Goutam, S. P., Saxena, M., Sahu, R., Kushwaha, H. S., & Tiwari, A. (2018). Green synthesis of TiO? nanoparticles using leaf extract of Jatropha curcas L. for photocatalytic degradation of tannery wastewater. Chemical Engineering Journal, 336, 386–396. https://doi.org/10.1016/j.cej.2017.12.029

Hanafy, M. S., El-Sayed, S., Ammar, R., & El-Maghraby, A. (2020). Green synthesis and characterization of TiO? nanoparticles using Aloe vera extract at different pH values. Scientific Journal of King Faisal University, 21(1), 103–110. https://doi.org/10.37575/b/sci/2020

Hassan, Q., Du, M., Liu, Y., Wu, Z., & Li, Q. (2024). The renewable energy role in the global energy transformations. Renewable Energy Focus, 48, 100545. https://doi.org/10.1016/j.ref.2024.100545

Imanieh, M. H., Ghoranneviss, M., Farnia, G., Esmaeili, A., & Hantehzadeh, M. R. (2010). Different morphologies of TiO? nanostructures in acidic and basic sol–gel method. Nano, 5(5), 279–285. https://doi.org/10.1142/S1793292010002189

Kabir, E., Kumar, P., Kumar, S., Adelodun, B., & Kim, K. H. (2018). Solar energy: Potential and future prospects. Renewable and Sustainable Energy Reviews, 82, 894–900. https://doi.org/10.1016/j.rser.2017.09.094

Karim, N. A., Sulaiman, M. Y., Khan, M. M. A., & Akhtaruzzaman, M. (2019). Nanostructured photoanode and counter electrode materials for efficient dye-sensitized solar cells (DSSCs). Solar Energy, 185, 165–188. https://doi.org/10.1016/j.solener.2019.04.057

Lee, K. X., Wong, W. S., Ahmad, M. K., & Zaman, S. (2019). Bio-mediated synthesis and characterisation of silver nanocarrier, and its potent anticancer action. Nanomaterials, 9(10), 1423. https://doi.org/10.3390/nano9101423

Liu, Q., & Wang, J. (2019). Dye-sensitized solar cells based on surficial TiO? modification. Solar Energy, 184, 454–465. https://doi.org/10.1016/j.solener.2019.04.032

Mohammadian-Sarcheshmeh, H., Arazi, R., & Mazloum-Ardakani, M. (2020). Application of bifunctional photoanode materials in DSSCs: A review. Renewable and Sustainable Energy Reviews, 134, 110249. https://doi.org/10.1016/j.rser.2020.110249

Mulay, M. R., Patwardhan, S. V., & Martsinovich, N. (2024). Review of bio-inspired green synthesis of titanium dioxide for photocatalytic applications. Catalysts, 14(11), 742. https://doi.org/10.3390/catal14110742

Muniandy, S. S., Adam, F., Mohamed Saad, M. Z., & Subramaniam, S. (2017). Green synthesis of mesoporous anatase TiO? nanoparticles and their photocatalytic activities. RSC Advances, 7(76), 48083–48094. https://doi.org/10.1039/C7RA08187A

Nethravathi, P. C., Kumar, M. A., Suresh, D., & Nagabhushana, H. (2021). TiO? and Ag–TiO? nanomaterials for enhanced photocatalytic and antioxidant activity: Green synthesis using Cucumis melo juice. Materials Today: Proceedings, 49, 841–848. https://doi.org/10.1016/j.matpr.2021.05.670

Priyono, B., Huda, A., Prasetyo, I., & Abdullah, M. (2018). Nanostructure properties and dye-sensitized solar cell open-circuit voltage of a TiO? aerogel and pre-hydrothermally treated xerogels. International Journal of Technology, 9(5), 972–982. https://doi.org/10.14716/ijtech.v9i5.1067

Qamar, O. A., Alhajri, M., Alsaidi, M., & Baig, M. M. A. (2024). Upgrading catalytic properties of green synthesized TiO? for green fuel production from apricot seeds oil. Fuel, 355, 129516. https://doi.org/10.1016/j.fuel.2023.129516

Saini, R., & Kumar, P. (2023). Green synthesis of TiO? nanoparticles using Tinospora cordifolia plant extract and its potential application for photocatalysis and antibacterial activity. Inorganic Chemistry Communications, 156, 111221. https://doi.org/10.1016/j.inoche.2023.111221

Sangeetha, A., Ambli, A., & Nagabhushana, B. M. (2024). Green and chemical synthesis of TiO? nanoparticles: An in-depth comparative analysis and photoluminescence study. Nano-Structures & Nano-Objects, 40, 101408. https://doi.org/10.1016/j.nanoso.2024.101408

Sarip, N. A., Aminudin, N. I., & Danial, W. H. (2022). Green synthesis of metal nanoparticles using Garcinia extracts: A review. Environmental Chemistry Letters, 20(1), 469–493. https://doi.org/10.1007/s10311-021-01319-3

Sasikumar, R., Shanmugam, R., Venkatesh, M., & Gopinath, K. (2024). Dye-sensitized solar cells: Insights and research divergence towards alternatives. Renewable and Sustainable Energy Reviews. https://doi.org/10.1016/j.rser.2024.114549

Saud, P. S., Rahman, M. M., Jilani, A., Shah, S. M., & Kim, H. (2024). Dye-sensitized solar cells: Fundamentals, recent progress, and optoelectrical properties improvement strategies. Optical Materials. https://doi.org/10.1016/j.optmat.2024.115242

Sawal, M. H., Rosli, M. I., Khan, M. M. R., & Yusoff, N. H. (2023). A review of recent modification strategies of TiO?-based photoanodes for efficient photoelectrochemical water splitting performance. Electrochimica Acta, 467, 143142. https://doi.org/10.1016/j.electacta.2023.143142

Shakeel-Ahmad, M., Pandey, A., & Abd-Rahim, N. (2017). Advancements in the development of TiO? photoanodes and its fabrication methods for dye-sensitized solar cell (DSSC) applications: A review. Renewable and Sustainable Energy Reviews, 77, 89–108. https://doi.org/10.1016/j.rser.2017.03.129

Singh, S., Kumar, V., Kaushal, A., & Sud, D. (2022). Green synthesis of TiO? nanoparticles using Citrus limon juice extract as a bio-capping agent for enhanced performance of dye-sensitized solar cells. Surfaces and Interfaces, 28, 101652. https://doi.org/10.1016/j.surfin.2021.101652

Sofyan, N., Muhammad, Ridhova, A., Angellinnov, F., M’rad, M., Yuwono, A. H., Dhaneswara, D., Priyono, B., & Fergus, J. W. (2025). Jasmine flowers extract-mediated green synthesis of TiO? nanoparticles and their photocurrent characteristics for dye-sensitized solar cell application. Materials for Renewable and Sustainable Energy, 14(2). https://doi.org/10.1007/s40243-025-00320-y

Sofyan, N., Ridhova, A., Yuwono, A. H., & Udhiarto, A. (2017). Fabrication of solar cells with TiO? nanoparticles sensitized using natural dye extracted from mangosteen pericarps. International Journal of Technology, 8(7), 1229–1238. https://doi.org/10.14716/ijtech.v8i7.692

Sofyan, N., Rilda, Y., & And, A. (2025). Sustainable synthesis of TiO? nanoparticles from gambier leaf extract for enhanced DSSC photocurrent response. Results in Materials, 27, 100752. https://doi.org/10.1016/j.rinma.2025.100752

Sridevi, D. V., Ramya Devi, K. T., Jayakumar, N., & Sundaravadivel, E. (2020). pH-dependent synthesis of TiO? nanoparticles exerts its effect on bacterial growth inhibition and osteoblast proliferation. AIP Advances, 10(9). https://doi.org/10.1063/5.0020029

Srikar, S., Giri, D., Pal, D., Mishra, P., & Upadhyay, S. (2016). Green synthesis of silver nanoparticles: A review. Green and Sustainable Chemistry, 6, 34–56. https://doi.org/10.4236/gsc.2016.61004

Talebzadeh, S., Queffélec, C., & Knight, D. (2019). Surface modification of plasmonic noble metal–metal oxide core–shell nanoparticles. Nanoscale Advances, 1(12), 4578–4591. https://doi.org/10.1039/c9na00581a

Thammaacheep, P., Suriwong, T., Jannoey, P., Khanitchaidecha, W., Nakaruk, A., & Channei, D. (2024). Bio-synthesis of TiO? photocatalyst: A reduced step approach using leaf extract. Green Chemistry Letters and Reviews, 17(1). https://doi.org/10.1080/17518253.2024.2433607

Tryba, B., Morawski, A., Przepiórski, J., Tsumura, T., & Toyoda, M. (2016). Influence of pH of sol–gel solution on phase composition and photocatalytic activity of TiO? under UV and visible light. Materials Research Bulletin, 84, 152–161. https://doi.org/10.1016/j.materresbull.2016.07.035

Uvarov, V., & Popov, I. (2007). Metrological characterization of X-ray diffraction methods for determination of crystallite size in nano-scale materials. Materials Characterization, 58(10), 883–891. https://doi.org/10.1016/j.matchar.2006.09.002

Virkutyte, J., & Varma, R. (2011). Green synthesis of metal nanoparticles: Biodegradable polymers and enzymes in stabilization and surface functionalization. Chemical Science, 2(5), 837–846. https://doi.org/10.1039/c0sc00338g

Wang, Y., He, Y., Lai, Q., & Fan, M. (2014). Review of the progress in preparing nano-TiO?: An important environmental engineering material. Journal of Environmental Sciences, 26(11), 2139–2177. https://doi.org/10.1016/j.jes.2014.09.023

Yalcin, M. (2022). The effect of pH on the physical and structural properties of TiO? nanoparticles. Journal of Crystal Growth, 585, 126603. https://doi.org/10.1016/j.jcrysgro.2022.126603

Ye, M., Wen, X., Wang, M., Iocozzia, J., Zhang, N., Lin, C., & Lin, Z. (2015). Recent advances in dye-sensitized solar cells: From photoanodes, sensitizers and electrolytes to counter electrodes. Materials Today, 18(3), 155–162. https://doi.org/10.1016/j.mattod.2014.09.001