Nanomaterials (NMs) have gained prominence in technological advancements due to their tunable physical, chemical and biological properties with enhanced performance over their bulk counterparts. NMs are categorized depending on their size, composition, shape, and origin. The ability to predict the unique properties of NMs increases the value of each classification. Due to increased growth of production of NMs and their industrial applications, issues relating to toxicity are inevitable. The aim of this review is to compare synthetic (engineered) and naturally occurring nanoparticles (NPs) and nanostructured materials (NSMs) to identify their nanoscale properties and to define the specific knowledge gaps related to the risk assessment of NPs and NSMs in the environment. The review presents an overview of the history and classifications of NMs and gives an overview of the various sources of NPs and NSMs, from natural to synthetic, and their toxic effects towards mammalian cells and tissue. Additionally, the types of toxic reactions associated with NPs and NSMs and the regulations implemented by different countries to reduce the associated risks are also discussed.

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Review on nanoparticles and nanostructured materials: history, sources, toxicity and regulations.

Mechanical and chemical recycling of solid plastic waste.

Synthesis methods for nanosized hydroxyapatite with diverse structures.

Once referred to as ‘materials of 1,000 uses’, plastics meet demands in everything from clothing and automotive sectors to the manufacturing of medical equipment and electronics. Concomitant with usage, worldwide generation of plastic solid waste increases daily and is currently around 150 million tonnes per annum. Although recycled materials may have physical properties similar to those of virgin plastics, the resulting monetary savings are limited and the properties of most plastics are significantly compromised after a number of processing cycles. An alternative approach to processing plastic solid waste is chemical recycling, the success of which relies on the affordability of processes and the efficiency of catalysts. In this Review, we describe technologies available for sorting and recycling plastic solid waste into feedstocks, as well as state-of-the-art techniques to chemically recycle commercial plastics. These evaluations are followed by a survey of recent advances in the design of new high-performing recyclable polymers. Many methods exist for the recycling of plastic solid waste. Chemical recycling, which can take many forms from high-temperature pyrolysis to mild, solution-based catalytic depolymerization, can afford enormous economic and environmental benefits. This Review covers the state of the art in chemical recycling and the design of high-performance polymers amenable to such processes.

Chemical recycling of waste plastics for new materials production

Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol–gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual...

Solution Combustion Synthesis of Nanoscale Materials

Recycling of PVC wastes

Hydroxyapatite nanorods as novel fillers for improving the properties of dental adhesives: Synthesis and application

Hydroxyapatite (HAp) is the major mineral constituent of vertebrate bones and teeth. It has been well documented that HAp nanoparticles can significantly increase the biocompatibility and bioactivity of man-made biomaterials. Over the past decade, HAp nanoparticles have therefore increasingly been in demand, and extensive efforts have been devoted to develop many synthetic routes, involving both scientifically and economically new features. Several investigations have also been made to determine how critical properties of HAp can be effectively controlled by varying the processing parameters. With such a wide variety of methods for the preparation of HAp nanoparticles, choosing a specific procedure to synthesize a well-defined powder can be laborious; accordingly, in the present review, we have summarized all the available information on the preparation methodologies of HAp, and highlighted the inherent advantages and disadvantages involved in each method. This article is focused on nanosized HAp, although recent articles on microsized particles, especially those assembled from nanoparticles and/or nanocrystals, have also been reviewed for comparison. We have also provided several scientific figures and discussed a number of critical issues and challenges which require further research and development.

Mehdi Sadat-Shojai

Papers

Synthesis methods for nanosized hydroxyapatite with diverse structures.

Recycling of PVC wastes

Hydroxyapatite nanorods as novel fillers for improving the properties of dental adhesives: Synthesis and application

Synthesis Methods for Nanosized Hydroxyapatite with Diverse Structures

Hydrothermal processing of hydroxyapatite nanoparticles—A Taguchi experimental design approach