A research has been conducted to investigate the physico-mechanical and microstructure properties of geopolymers synthesised from metakaolin activated with sodium silicate solution. A wide range of physical and mechanical properties of geopolymers were studied such as bulk density, porosity, Vickers hardness, compressive strength, thermal expansion and thermal conductivity. It was found that these properties were directly related to geopolymers process variables such as Si:Al, Na:Al, Na₂O:H₂O, time and curing temperature. The structure of the resulting geopolymers was studied by using X-Ray diffraction (XRD) and the microstructure of geopolymers paste and the interfacial transition zone (ITZ) between the aggregate and the matrix of geopolymer were studied by using Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM). The results gave a new insight into the composition-microstructure-property relationship of geopolymers and paving the way to the production of geopolymers with improved performance in a variety of applications.

The goal of this research is to synthesize and characterize Fe₃O₄@Chitosan-AgNP nanocomposites in order to determine their antibacterial activity. The research methods include the synthesis of Fe₃O₄@Chitosan-AgNP nanocomposites, as well as the characterization of nanoparticles using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) analysis, and subsequent antibacterial activity tests. The study’s findings demonstrated the successful synthesis of Fe₃O₄@Chitosan-AgNP nanocomposites, followed by nanoparticle characterization using SEM, TEM, XRD, and FTIR. Based on the XRD results, the conjugation of Fe₃O₄@Chitosan-AgNP nanocomposites has been successfully formed, as evidenced by the appearance of characteristic peaks of Fe₃O₄, chitosan, and AgNPs. According to the FTIR results, the interaction between chitosan-AgNPs and conjugated Fe₃O₄ occurred via the N atom in the NH₂ group and the O atom in the OH group, and C=O. The SEM and TEM images also show that the Fe₃O₄@Chitosan-AgNP conjugation is a nanoparticle-based composite material. The combination of nanocomposites Fe₃O₄@Chitosan-AgNPs has antibacterial activity, inhibiting the growth of bacteria such as Bacillus cereus and Escherichia coli.

This is the first of two papers about the synthesis and microstructure properties of the Geo–rGO–TiO₂ ternary nanocomposite, which was designed to suit the criteria of a pervaporation membrane for seawater desalination. The performance and capability of Geo–rGO–TiO₂ as a seawater desalination pervaporation membrane are described in the second paper. A geopolymer made from alkali-activated metakaolin was utilized as a binder for the rGO-TiO₂ nanocomposite. A modified Hummer’s method was used to synthesize graphene oxide (GO), and a hydrothermal procedure on GO produced reduced graphene oxide (rGO). The adopted approach yielded high-quality GO and rGO, based on Raman spectra results. The nanolayered structure of GO and rGO is revealed by Transmission Electron Microscopy (TEM) images. The Geo–rGO–TiO₂ ternary nanocomposite was created by dispersing rGO nanosheets and TiO₂ nanoparticles into geopolymer paste and stirring it for several minutes. The mixture was then cured in a sealed mold at 70 °C for one hour. After being demolded, the materials were kept for 28 days before being characterized. Fourier Transform Infrared (FTIR) and X-ray Diffraction (XRD) measurements revealed that the geopolymer matrix efficiently bonded the rGO and TiO₂, creating nanocomposites. Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) was used to examine the morphology of the outer layer and cross-sections of nanocomposites, and the results displayed that rGO were stacked on the surface as well as in the bulk of the geopolymer and will potentially function as nanochannels with a width of around 0.36 nm, while TiO₂ NPs covered the majority of the geopolymer matrix, assisting in anti-biofouling of the membranes. The pores structure of the Geo–rGO–TiO₂ were classified as micro–meso pores using the Brunauer–Emmet–Teller (BET) method, indicating that they are appropriate for use as pervaporation membranes. The mechanical strength of the membranes was found to be adequate to withstand high water pressure during the pervaporation process. The addition of rGO and TiO₂ NPs was found to improve the hyropobicity of the Geo–rGO–TiO₂ nanocomposite, preventing excessive seawater penetration into the membrane during the pervaporation process. The results of this study elucidate that the Geo–rGO–TiO₂ nanocomposite has a lot of potential for application as a pervaporation membrane for seawater desalination because all of the initial components are widely available and inexpensive.

Immobilization of heavy metal ions using geopolymer paste is a promising way to solve the problem with heavy metal waste from industries. This research focused on the immobilization of Pb²⁺ and Cd²⁺ which are common heavy metal waste with distinctive cation size. The cations were immobilized by geopolymerization process to form geopolymer paste. The paste was prepared by using fly ash from a power plant in Cilacap, Indonesia, with SiO₂/Al₂O₃ ratio = 3 and S/L = 1.6. According to XRF analysis, the ash is type C fly ash and additional Al(OH)₃ was needed to achieve the SiO₂/Al₂O₃ ratio. A solution of Cd²⁺ or Pb²⁺ from their respective nitrate salts was added to the geopolymer mixture to make an immobilized Cd²⁺ or Pb²⁺ in a fly ash geopolymer matrix. Compressive strength tests showed that the maximum strength was achieved when 3855 ppm of Cd²⁺ or 765 ppm of Pb²⁺ was added to the geopolymer mixture. The change of strength is explained to be caused by the filling of geopolymer cavities that were formed during the geopolymerization process. Due to the smaller size of Cd²⁺ than Pb²⁺, the strongest geopolymer paste was achieved at higher Cd²⁺ concentration than Pb²⁺. X-ray diffraction analyses results show that the addition of Cd²⁺ or Pb²⁺ shift the position on hump to larger 2θ.

This is part 2 of the research on pervaporation membranes for seawater desalination based on Geo–rGO–TiO₂ nanocomposite. The quality of the Geo–rGO–TiO₂ pervaporation membranes (PV), as well as the suitability of the built pervaporation system, is thoroughly discussed. The four membranes described in detail in the first article were tested for their capabilities using the parameters turbidity, salinity, total suspended solids (TSS), and electrical conductivity (EC). The membranes’ flux permeate was measured as a function of temperature, and salt rejection was calculated using the electrical conductivity values of the feed and permeate. Fourier-transform infrared (FTIR) and X-ray diffraction (XRD) techniques were used to investigate changes in the chemical composition and internal structure of the membranes after use in pervaporation systems. The morphology of the membrane’s surfaces was examined by means of scanning electron microscopy (SEM), and the elemental distribution was observed by using X-ray mapping and energy dispersive spectroscopy (EDS). The results showed that the pervaporation membrane of Geo–rGO–TiO₂ (1, 3) achieved a permeate flux as high as 2.29 kg/m²·h with a salt rejection of around 91%. The results of the FTIR and XRD measurements did not show any changes in the functional group and chemical compositions of the membrane after the pervaporation process took place. Long-term pressure and temperature feed cause significant cracking in geopolymer and Geo–TiO₂ (3) membranes. SEM results revealed that the surface of all membranes is leached out, and elemental distribution based on X-ray mapping and EDS observations revealed the addition of Na+ ions on the membrane surface. The study’s findings pave the way for more research and development of geopolymers as the basic material for inorganic membranes, particularly with the addition of rGO–TiO₂ nanocomposites.