Biodegradable Polymer Matrix Composites Containing Graphene-Related Materials for Antibacterial Applications: A Critical Review.

For the first time, the present review critically evaluates biodegradable polymer matrix composites containing graphene-related materials (GRMs) for antibacterial applications while discussing their development, processing routes, mechanical properties, and antibacterial activity. Due to its suitable biological properties and processability, chitosan has been the most widely used biodegradable polymer for the fabrication of GRM-containing composites with antibacterial properties. The majority of biodegradable polymers (including cellulose-, gelatine-, PVA-, PCL-, and PHA-based polymers) exhibit little to no antibacterial effect alone; however, they show significant antibacterial activity (>70%) when combined with GRMs. In vitro and in vivo studies indicate that GRMs functionalization with biodegradable polymers also reduces potential GRM cytotoxicity. Overall, GRMs in biodegradable polymer matrices provide attractive antibacterial activity against a broad spectrum of bacteria (>30 different bacteria) along with improved mechanical properties over pristine polymers, where the type and the degree of improvement provided by GRMs depend on the specific matrix. For example, the addition of GRMs into chitosan, PVA, and PCL matrices increases their tensile strength by 80%, 180%, and 40%, respectively. Challenges remain in understanding the effects of processing routes and post-processing methods on the antibacterial activity and biocompatibility of biodegradable polymer/GRM composites. Given their promising properties and functionality, research on these composites is expected to further increase along with the implementation of new composite systems. These would include a wide range of applications, e.g., wound dressings, tissue engineering, drug delivery, biosensing, and photo-thermal therapy, as well as non-medical use, e.g., antibacterial food packaging, water treatment, and antibacterial fabrics. STATEMENT OF SIGNIFICANCE: Graphene-related materials (GRMs) in polymer matrices can provide excellent antibacterial activity against a broad spectrum of bacteria together with improved mechanical properties (e.g., tensile strength and elastic modulus) over pristine polymers; thus, research efforts and applications of biodegradable polymer matrix composites containing GRMs have increased notably in the last ten years. For the first time, the present review critically evaluates biodegradable polymer matrix composites containing GRMs for antibacterial applications while discussing their development, processing routes, mechanical properties, and antibacterial activity. Future research directions for each composite system are proposed to shed light on overcoming the existing challenges in composite performance (e.g., mechanical properties, toxicity) reported in the literature.

A systematic study for removal of heavy metals from aqueous media using Sorghum bicolor: an efficient biosorbent.

This review is based on the adsorption characteristics of sorghum (Sorghum bicolor) for removal of heavy metals from aqueous media. Different parameters like pH, temperature of the medium, sorghum concentration, sorghum particle size, contact time, stirring speed and heavy metal concentration control the adsorption efficiency of sorghum biomass for heavy metal ions. Sorghum biomass showed maximum efficiency for removal of heavy metal ions in the pH range of 5 to 6. It is an agricultural waste and is regarded as the cheapest biosorbent, having high adsorption capacity for heavy metals as compared to other reported adsorbents, for the treatment of heavy metal polluted wastewater. Adsorption of heavy metal ions onto sorghum biomass follows pseudo second order kinetics. Best fitted adsorption isotherm models for removal of heavy metal ions on sorghum biomass are Langmuir and Freundlich adsorption isotherm models. Thermodynamic aspects of heavy metal ions adsorption onto sorghum biomass have also been elaborated in this review article. How adsorption efficiency of sorghum biomass can be improved by different physical and chemical treatments in future has also been elaborated. This review article will be highly useful for researchers working in the field of water treatment via biosorption processing. The quantitative demonstrated efficiency of sorghum biomass for various heavy metal ions has also been highlighted in different sections of this review article.