Clinoptilolite modified by hexadecyltrimethylammonium bromide (HDTMA-Br) was used to simultaneously remove copper and hexavalent chromium from aqueous solutions. The surface properties of HDTMA-modified natural zeolite (HMNZ) were characterized using SEM, BET, Zeta potential and FTIR techniques. SEM images showed that surfactant is adsorbed on the surface of the zeolite, which is confirmed by the FTIR result. The results from BET demonstrated a reduction in the specific surface area and pore volume due to the presence of surfactant molecules on the external surface of zeolite. The effects of important parameters on adsorption efficiency of Cu2+ and Cr (VI) were evaluated by Box-Behnken design. The Langmuir isotherm provided the best fit to the equilibrium data of Cu2+ and Cr (VI), with the maximum adsorption capacity of 0.068 and 0.0093(mmol), respectively. The film diffusion mechanism was found to control the mass transfer, and the adsorption reactions were computed as endothermic for Cu2+ ( = 17.58 kJ) and exothermic for Cr (VI) ( −26.18 kJ). The results indicated that surfactant modification changes the surface charge of zeolite from negative to positive, which makes zeolites economic adsorbents with the possibility of simultaneous removal of cations and oxyanions. The results also showed that the removal efficiency of Cr (VI) increases in the presence of copper cations due to there being more positive sites on the adsorbent surface.

Materials at the nanoscale show exciting and different properties. In this review, the applications of nanomaterials for modifying the main components of microbial fuel cell (MFC) systems (i.e., electrodes and membranes) and their effect on cell performance are reviewed and critically discussed. Carbon and metal-based nanoparticles and conductive polymers could contribute to the growth of thick anodic and cathodic microbial biofilms, leading to enhanced electron transfer between the electrodes and the biofilm. Extending active surface area, increasing conductivity, and biocompatibility are among the significant attributes of promising nanomaterials used in MFC modifications. The application of nanomaterials in fabricating cathode catalysts (catalyzing oxygen reduction reaction) is also reviewed herein. Among the various nanocatalysts used on the cathode side, metal-based nanocatalysts such as metal oxides and metal-organic frameworks (MOFs) are regarded as inexpensive and high-performance alternatives to the conventionally used high-cost Pt. In addition, polymeric membranes modified with hydrophilic and antibacterial nanoparticles could lead to higher proton conductivity and mitigated biofouling compared to the conventionally used and expensive Nafion. These improvements could lead to more promising cell performance in power generation, wastewater treatment, and nanobiosensing. Future research efforts should also take into account decreasing the production cost of the nanomaterials and the environmental safety aspects of these compounds.

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Management of the produced heat has been one of the challenges encountered in the oxidative coupling of methane (OCM) process. In this study, the influence of the thermal conductive tubular reactor on the total productivity and selectivity of OCM was investigated. The reactors were made from three different metal compounds: two stainless steel tubes and one gold-coated copper tube, and their impact on the operating conditions was compared. 5% Li/MgO was prepared as a catalyst for OCM and characterized by XRD, CO2-TPD, FTIR, and BET. In addition, the effect of reactor geometry on the oxidative coupling process was investigated experimentally in the single channel and multi-channel reactors with different hydraulic diameters.