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Biodiesel is generally obtained by transesterification and esterification of appropriate feedstocks facilitated by a catalyst. It has emerged to be one of the most potential alternatives for the conventional fuels gaining worldwide attention. Heterogeneous catalysts are usually preferred than homogeneous for biodiesel synthesis due to facile separation and insignificant soap formation. However, the separation still possesses difficulty leading to mass transfer hindrance. Therefore, these catalysts can be further modified using magnetic separation techniques to develop magnetically separable catalysts. The magnetic nanoparticles (MNPs) are notable appealing catalysts due to huge surface area, high activity, amicable functional groups and structures, adaptable properties, conformity in pore size, and facile separation have made them desirable catalyst carriers for biodiesel synthesis. The MNPs are modified via functionalization to construct magnetically recoverable heterogeneous nanocatalysts. Magnetic catalysts can be utilized as a befitting option for biodiesel synthesis as these are environmentally benign, highly reusable and economically viable. The current review article discusses different magnetic solid catalysts such as magnetic base, acid, biocatalysts and bifunctional of acid base catalysts for efficient biodiesel synthesis. The prime focus of this paper rest on the catalytic performances of various magnetically recoverable catalysts, mechanisms and recyclability for biodiesel production processes. The synthesis methods of magnetic heterogeneous base and acid nanocatalysts, magnetic properties, functionalization and their reciprocity on the catalytic activity are reviewed in this article.

Biodiesel is considered eco-friendly, biodegradable, non-toxic, and carbon-neutral fuel. It is made from edible or non-edible oil feedstocks including other triglyceride sources. The production of biodiesel depends on the availability of a particular feedstock and the cost of desired raw materials. Biodiesel is mainly produced by the transesterification process using a suitable catalyst preferably a heterogeneous catalyst as it is more beneficial in terms of reusability, recovery, product purity, and production cost as well. Various reactors are developed to produce cost-effective biodiesel at the commercial level. The latest trend in biodiesel synthesis is the application of the machine learning (ML) technique to optimize the process parameters. The application of a mixture of two or more oils as feedstock either non-edible or edible oil is emphasized for biodiesel synthesis and is presently getting more importance. In this paper, the production of biodiesel from various mixed oil (hybrid oil) is reviewed and the effects of mixed oil on the reaction, physicochemical properties, fatty acid composition, and fuel quality of the product are discussed. The study highlighted the activity of various catalysts in the reaction of mixed oil and the economic feasibility. It was found that the ratio of mixed oil is an important factor in terms of conversion and quality of biodiesel. It is also revealed that the application of the ML technique is essentially useful to optimize production efficiency. The utilization of mixed oils will overcome the issues related to the non-availability of feedstocks and reduce the overall cost with improved quality of biodiesel. This approach enhances the production possibility of biodiesel at a large-scale and may boost the biorefinery sector satisfying the future energy demand if the research at the advanced level goes in the right direction.

Metal free room temperature phosphorescent materials have been the subject of considerable attention due to their potential applications in optoelectronic devices sensing, and security and safety signage. This study discusses how efficient fluorescent and phosphorescent chlorine doped carbon nitride dots (Cl-CNDs) were prepared by thermal treatment of guanidine hydrochloride. The Cl-CNDs prepared were characterized by field emission scanning electron microscope, dynamic light scattering, PXRD, EDX, Thermo gravimetric analysis, FT-IR, and UV-Visible spectroscopy. The Cl-CNDs exhibit a long phosphorescence lifetime of 657 ms and the phosphorescence quantum yield was found to be 2.32% upon being excited at 360 nm in ambient conditions. Formation of compact coreparticles via condensation along with hydrogen bonding of Cl-CNDs by its functional groups facilitate intersystem crossing and stabilizes the triplet states, favoring room temperature phosphorescence. The cost effective preparation and tunable optical properties of Cl-CNDs may find applications in security encryption and optoelectronic devices.