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Heavy metal pollution of water is a global concern, which adversely affects human health because of its resistance to biodegradation and thus its transmission in the food chain via bioaccumulation. Nano zerovalent iron (nZVI) is very effective for the removal of heavy metals and is cost effective in terms of production. However, the main problems of nZVI are agglomeration and ease of oxidation. Several stabilization materials have been implemented to limit the aggregation of nZVI, such as silica, activated carbon and biochar. In comparison, as a support material, biochar possesses a large surface area, high stability and strong adsorption capacity, as well as being obtainable from various types of materials. Thus, this work aims to establish the opportunities available on the use of biochar-supported nZVI in utilizing its ability to stabilize and immobilize the nZVI. This review also reports the preparation, modification and surface enhancement of biochar, nZVI and biochar-nZVI for practical use as adsorbents. This review shows that modifications of the nZVI surface can help in their stabilization and reduction of aggregation. Additionally, this review is able to increase one's understanding of heavy metal sorption behavior by biochar-supported nZVI as it is the important as heavy metal sorption is driven based on biochar-nZVI type and heavy metal species which involve numerous mechanisms, including physical binding, complexation, ion exchange, surface precipitation and electrostatic interactions. Furthermore, this research reviews the adsorption parameters, including the crucial adsorption mechanism of heavy metals onto biochar-nZVI; the reusability of the biochar-nZVI is also discussed in this work.

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Regenerated cellulose membrane (RCM) was successfully fabricated via the dissolution systems of 7 wt % NaOH/12 wt % urea. Extraction of cellulose sourced from recycled newspapers was done after undergoing alkali and NaClO 2 treatment. The membrane was characterized by using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray analysis (EDAX). The capability of the membrane to act as the adsorbent was applied for the adsorption of chromium(VI) from aqueous solution. The Cr(VI) adsorption onto RCM was tested under different parameters, including the pH of the solution, the initial Cr(VI) concentration, and the contact time. The changes on the adsorbent after the adsorption of Cr(VI) was analyzed by using FTIR and SEM-EDAX. The optimum condition for the adsorption of Cr(VI) was noted at pH 2 for 100 ppm of Cr (VI) in duration of 12 h with the optimum percentage removal of 18.1278 mg/g. The behavior of the adsorption process and adsorption kinetics were best-fitted with the Langmuir model and the pseudo-first order model, respectively.

Due to the rapid development of industrialization over the years, the enhancement on heavy metals removal technology are becoming more urgent. Graphene oxide (GO) gained attention as adsorbents due to high surface area and high affinity towards heavy metals removal. However, its tendency for agglomeration and difficulty in phase separation urges more researches done to address its drawback. Zinc oxide (ZnO), a versatile nanomaterial, has been discovered to have high affinity towards heavy metals removal, tendency to spread out across GO sheet and ease of handling. Therefore, in this study, zinc oxide/graphene oxide nanocomposites (ZnO/GO) were synthesized as adsorbents for the removal of Pb(II) from aqueous solution. The synthesized composite was characterized using Fourier-transform Infrared Spectrometry (FT-IR), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), and had confirmed the chemically bonding of ZnO on GO. From the batch test, the optimum adsorbent dosage and initial pH for Pb(II) adsorption using ZnO/GO were 0.16 g/L and at pH 5, respectively, with the adsorption capacity of Pb(II) at 418.78 mg/g. The most rapid adsorption had occurred in the first 30 minutes, and the equilibrium time was achieved at 160 minutes. Also, Pb(II) adsorption had followed the pseudo-first order kinetic model. Therefore, ZnO/GO is thought to be a newly promising adsorbent in removing Pb(II) ion from the aqueous solution.

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