The focus of current research in material science has shifted from “less efficient” single-component nanomaterials to the superior-performance, next-generation, multifunctional nanocomposites. TiO₂ is a widely used benchmark photocatalyst with unique physicochemical properties. However, the large bandgap and massive recombination of photogenerated charge carriers limit its overall photocatalytic efficiency. When TiO₂ nanoparticles are modified with graphene quantum dots (GQDs), some significant improvements can be achieved in terms of (i) broadening the light absorption wavelengths, (ii) design of active reaction sites, and (iii) control of the electron-hole (e⁻-h⁺) recombination. Accordingly, TiO₂-GQDs nanocomposites exhibit promising multifunctionalities in a wide range of fields including, but not limited to, energy, biomedical aids, electronics, and flexible wearable sensors. This review presents some important aspects of TiO₂-GQDs nanocomposites as photocatalysts in energy and biomedical applications. These include: (1) structural formulations and synthesis methods of TiO₂-GQDs nanocomposites; (2) discourse about the mechanism behind the overall higher photoactivities of these nanocomposites; (3) various characterization techniques which can be used to judge the photocatalytic performance of these nanocomposites, and (4) the application of these nanocomposites in biomedical and energy conversion devices. Although some objectives have been achieved, new challenges still exist and hinder the widespread application of these nanocomposites. These challenges are briefly discussed in the Future Scope section of this review.

Major barriers to the implementation of nanotechnology include reproducible synthesis and scalability. Batch solution phase methods do not appear to have the potential to overcome these barriers. Microfluidic methods have been investigated as a means to enable controllable and reproducible synthesis; however, the most popular constituent of microfluidics, polydimethylsiloxane, is ill-suited for mass production. Multi-inlet vortex mixers (MIVMs) have been proposed as a method for scalable nanoparticle production; however, the control and reproducibility of the nanoparticle is wanting. Here, we investigate the ability to improve the control and reproducibility of nanoparticles produced by using 3D printed MIVMs with herringbone patterns in the flow channels. We compare three methods, viz., microfluidic, MIVM, and herringbone-patterned MIVM methods, for the synthesis of lipid–polymer hybrid nanoparticles (LPHNPs). The 3D printed herringbone-patterned MIVM method resulted in the smallest LPHNPs with the most uniform size distribution and shows more reproducible results as compared to the other two methods. To elucidate the mechanism underlying these results, concentration slices and vorticity streamlines of mixing chambers have been analyzed for 3D printed herringbone-patterned MIVM devices. The results bode well for LPHNPs, a formulation widely investigated for its improved therapeutic efficacy and biocompatibility. The herringbone-patterned device also has the potential to be broadly applied to many solution phase processes that take advantage of efficient mixing. The methods discussed here have broad implications for reproducible production of nanoparticles with constituents such as siRNA, proteins, quantum dots, and inorganic materials.