In recent years, in an attempt to substitute the conventional synthetic sound absorption material, natural fibers and their sound absorption properties have been increasingly studied. This is due to the fact that conventional synthetic fiber has potential health risks for human beings and significant environmental impact. In this review, existing and newly emerging natural fiber sound absorbers are summarized and highlighted in three categories: raw material, fiber assembly and composite. The sound absorption mechanism, several widely used prediction models and the popular acoustic characterization methods are presented. The comparison of sound absorption properties between some natural sound absorbers and glass fiber is conducted in two groups, i.e., thin material and thick material. It is found that many natural fibers have comparable sound absorption performance, some of them can be the ideal alternatives to glass fiber, such as kapok fiber, pineapple-leaf fiber and hemp fiber. Last, the conclusion part of this review gives an outlook regarding the promotion of the commercial use of natural fiber by means of theoretical study, efficient and environmentally friendly pretreatment and Life Cycle Assessment.

Zinc oxide (ZnO) based nanostructures have gained remarkable attention worldwide for their photocatalytic activation behavior as a semi-conductor metal oxide photocatalyst in different industries, i.e. paints, cosmetic, rubber and composites coating. The main motivation of this thematic review is to analyze the mechanism of photocatalytic activity of ZnO nanostructures (ZONSs) in detail, and their application in photovoltaic, biomedical and sensing fields based on photocatalytic performance and other crucial properties that enable nano ZnO as a potential and competitive candidate in commercial markets. ZONSs were characterized with a wide range of analytical tools including X-ray diffraction (XRD), electron microscopies (SEM, FESEM, TEM), dynamic light scattering (DLS) and UV–VIS spectroscopy etc. These characterization tools provide us typical information about the crystal structure, level of crystallinity, shape, size, dimension and the change in physical, optical and chemical properties of ZONSs. Synthesis routes, process variables and their combined effect on the performance characterization of ZONSs have also been discussed in detail. The aim of this review is to provide an up-to-date knowledge to the readers about the applications of nano ZnO in diverse industries either in catalytic or in sensing form.

This paper discusses the influence of fiber reinforcement on the properties of geopolymer concrete composites, based on fly ash, ground granulated blast furnace slag and metakaolin. Traditional concrete composites are brittle in nature due to low tensile strength. The inclusion of fibrous material alters brittle behavior of concrete along with a significant improvement in mechanical properties i.e., toughness, strain and flexural strength. Ordinary Portland cement (OPC) is mainly used as a binding agent in concrete composites. However, current environmental awareness promotes the use of alternative binders i.e., geopolymers, to replace OPC because in OPC production, significant quantity of CO₂ is released that creates environmental pollution. Geopolymer concrete composites have been characterized using a wide range of analytical tools including scanning electron microscopy (SEM) and elemental detection X-ray spectroscopy (EDX). Insight into the physicochemical behavior of geopolymers, their constituents and reinforcement with natural polymeric fibers for the making of concrete composites has been gained. Focus has been given to the use of sisal, jute, basalt and glass fibers.

This present study proposed a successful one pot synthesis of zinc oxide nanoparticles (ZnO NPs) and their optimisation for photocatalytic applications. Zinc chloride (ZnCl₂) and sodium hydroxide (NaOH) were selected as chemical reagents for the proposed study. The design of this experiment was based on the reagents’ amounts and the ultrasonic irradiations’ time. The results regarding scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy confirmed the presence of ZnO NPs with pure hexagonal wurtzite crystalline structure in all synthesised samples. Photocatalytic activity of the developed samples was evaluated against methylene blue dye solution. The rapid removal of methylene blue dye indicated the higher photocatalytic activity of the developed samples than untreated samples. Moreover, central composite design was utilised for statistical analysis regarding the obtained results. A mathematical model for the optimisation of input conditions was designed to predict the results at any given point. The role of crystallisation on the photocatalytic performance of developed samples was discussed in detail in this novel study.