Titanium dioxide nanoparticles (TiO₂-NPs) were synthesized using the molten salt method and systematically characterized. TiO₂-NPs were evaluated for their capacity to promote the growth of Capsicum annuum cultivars together with the plant growth-promoting microorganisms (PGPMs) Bacillus thuringiensis (Bt) and Trichoderma harzianum (Th). The variables analyzed included physiological parameters and antioxidant responses. The capacity of TiO₂-NPs to scavenge free radicals was also investigated, along with their biocompatibility, using Artemia salina as an in vivo model. The results demonstrated that TiO₂-NPs exhibited a nanocuboid-type morphology, negative surface charge, and small surface area. It was noted that TiO₂-NPs enhanced the CFU and spore production of Bt (1.56–2.92 × 10⁸ CFU/mL) and Th (2.50–3.90 × 10⁸ spores/mL), respectively. It was observed that TiO₂-NPs could scavenge DPPH, ABTS, and H₂O₂ radicals (IC₅₀ 48.66–109.94 μg/mL), while not compromising the viability of A. salina at 50–300 μg/mL. TiO₂-NPs were determined to enhance the root length and fresh and dry weights of chili peppers. Similarly, TiO₂-NPs in synergy with Bt and Th increased the activity of β-1,3-Glucanase (2.45 nkat/g FW) and peroxidase (69.90 UA/g FW) enzyme activity, and increased the TPC (29.50 GA/g FW). The synergy of TiO₂-NPs with the PGPMs consortium also upregulated the total chlorophyll content: 210.8 ± 11.4 mg/mg FW. The evidence from this study unveils the beneficial application of TiO₂-NPs with Bt and Th as an efficient approach to promote the physiology and antioxidant responses of chili peppers.

Traditional methods of synthesizing nanoparticles often rely on physical and chemical processes using synthetic hazardous chemicals. In contrast, the rise in green chemistry emphasizes using bioactive compounds from plants for the eco-friendly synthesis of nanostructures. These green synthesis techniques are increasingly recognized for their simplicity, cost-effectiveness, and ability to yield non-toxic by-products, an approach that aligns with sustainable practices. In this research, a straightforward, cheap, environmentally friendly, and sustainable procedure was developed to fabricate Zinc oxide nanoparticles (ZnO-NPs) employing three different pulp extracts: Agave (Agave americana), Chiku (Manilkara zapota), and Soursop (Annona muricata) to serve in the synthesis as capping, reduction, or stabilization agent. Analytical characterization techniques confirmed the successful phytosynthesis of ZnO-NPs, evidenced by significant absorbance peaks of UV-Vis spectra at 362 nm, and the chemical composition of ZnO without noticeable traces of phytochemical residues by carrying out ATR-FTIR analysis. SEM, STEM microscopies, and XRD analysis verified that the ZnO nanoparticles possess spherical geometries and hexagonal crystal structures. The average size of these nanoparticles was around 15.94, 18.08, and 23.32 nm for Agave, Chiku, and Soursop extract-based synthesis, respectively. Additionally, the in vitro antibacterial activity of phytosynthetized ZnO-NPs was evaluated against E. coli and S. aureus, confirming effective bacterial growth inhibition and demonstrating their significant antimicrobial potential.

In this study, titanium dioxide nanoparticles (TiO₂-NPs) were produced via green routes using blueberry extracts obtained with isopropanol (I-TiO₂-NPs) and methanol (M-TiO₂ NPs). HPLC-DAD confirmed phenolic/flavonoid profiles in the extracts, and spectroscopy/microscopy established anatase, polyhedral, mesoporous TiO₂-NPs with Eg ≈ 3.0 eV, hydrodynamic sizes ≈ 130–150 nm and negative ζ-potentials (−33 to −50 mV). The in vitro compatibility between TiO₂-NPs and the plant-growth-promoting microorganisms (PGPMs) Bacillus subtilis (Bs), Bacillus thuringiensis (B), and Trichoderma harzianum (T) sustained increased growth up to 150 µg/mL without visible negative effects. In greenhouse experimentation of Capsicum annuum exposed to low-moderate TiO₂-NPs, an increased leaf number and plant height were observed, while root length did not exceed the controls. I-TiO₂ at moderate concentrations, particularly with a single PGPM (B or T), promoted fresh and dry biomass accumulation. Biochemically, peroxidase rose sharply for M-TiO₂ at a low dose with consortium, whereas I-TiO₂ elicited broader antioxidant responses; total protein increased at higher doses for both formulations, and total chlorophyll was highest with I-TiO₂ (high dose with or without PGPMS). Collectively, the nano-bio system shows a formulation- and dose-dependent biphasic behavior: (I) I-TiO₂ enhances biomass and photosynthetic pigments; (II) M-TiO₂ favors strong POX induction under specific microorganism-dose combinations; and (III) single PGPM co-application with I-TiO₂-NPs or M-TiO₂ NPs outperforms consortia under our experimental conditions. Green synthesis thus provides surface functionalities that improve dispersion, microbial compatibility, and predictable physiological/biochemical outcomes for precision agriculture.