A mini review of enzyme-induced calcite precipitation (EICP) technique for eco-friendly bio-cement production.

This paper has presented a mini review of previously published articles dealing with bio-cement production using enzyme-induced calcite precipitation (EICP) technique. EICP is a biological, sustainable, and natural way of producing calcite without the direct involvement of microorganisms from urea and calcium chloride using urease enzyme in water-based solution with minimum energy consumption and eco-friendly. Calcite is a renewable bio-material that acts as a binder to improve the mechanical properties of soils like strength, stiffness, and water permeability. EICP has many real applications such as fugitive duct control with low cost comparing with water application or pouring, self-healing cracked concretes, and upgrade or change the low-volume road surfaces that are difficult for road constructions. The crystal structure of finally produced calcium carbonate (CaCO3), calcite is affected by the source of calcium ion; the calcite produced from calcium chloride has a rhombohedral crystal structure. The urease enzyme used for EICP applications could be produced in a laboratory-scale from different plant species, bacteria, some yeasts, fungi, tissues of humans, and invertebrates. Nevertheless, urease enzyme produced from jack beans has showed urease enzyme activity around 2700-3500U/g, and the tendency to replace the urease enzyme found in the global market. All urease enzymes have 12-nm size, and this smaller size makes EICP preferable for all types of soil or sands including fine and silt sands.

Modified Membranes for Redox Flow Batteries-A Review.

In this review, the state of the art of modified membranes developed and applied for the improved performance of redox flow batteries (RFBs) is presented and critically discussed. The review begins with an introduction to the energy-storing chemical principles and the potential of using RFBs in the energy transition in industrial and transport-related sectors. Commonly used membrane modification techniques are briefly presented and compared next. The recent progress in applying modified membranes in different RFB chemistries is then critically discussed. The relationship between a given membrane modification strategy, corresponding ex situ properties and their impact on battery performance are outlined. It has been demonstrated that further dedicated studies are necessary in order to develop an optimal modification technique, since a modification generally reduces the crossover of redox-active species but, at the same time, leads to an increase in membrane electrical resistance. The feasibility of using alternative advanced modification methods, similar to those employed in water purification applications, needs yet to be evaluated. Additionally, the long-term stability and durability of the modified membranes during cycling in RFBs still must be investigated. The remaining challenges and potential solutions, as well as promising future perspectives, are finally highlighted.

Humic acid removal using cellulose acetate membranes grafted with poly (methyl methacrylate) and aminated using tetraethylenepentamine.

Graft copolymerization of cellulose acetate (CA) and poly (methyl methacrylate) (PMMA) was synthesized through free radical polymerization in the presence of cerium sulfate (CS) as initiator under nitrogen atmosphere in an aqueous solution. During the grafting reactions, the effects of polymerization time and temperature on the grafting were investigated. Furthermore, functionalization of the synthesized product was done using amine group (tetraethylenepentamine, TEPA). The results from Nuclear Magnetic Resonance (1H NMR) spectra confirmed a successful grafting of PMMA on the CA membrane surfaces. Zeta potential (ζ), field emission scanning electron microscopy (FESEM), and atomic absorption spectrophotometer (AAS) characterization studies were done. The maximum removal efficiencies for un-grafted CA (un-g-CA), CA-g-PMMA, and CA-g-PMMA-TEPA membranes at pH of 7.0 were 34.5%, 83.3%, and 99.1%, respectively. The removal percentage results were detected to increase with increasing in the regeneration cycles. At the end of the fourth cycle, the HA removal percentages were 41.6%, 87.4%, and 99.9% for un-g-CA, CA-g-PMMA and CA-g-PMMA-TEPA membranes, respectively.

Removal of chromium (VI) ions from aqueous solutions using amine-impregnated TiO2 nanoparticles modified cellulose acetate membranes.

In this work, TiO2 nanoparticles (NPs) were modified using tetraethylenepentamine (TEPA), ethylenediamine (EDA), and hexamethylenetetramine (HMTA) amines using impregnation process. The prepared amine modified TiO2 samples were explored as an additive to fabricate ultrafiltration membranes with enhanced capacity towards the removal of chromium ions from aqueous solution. Modified membranes were prepared from cellulose acetate (CA) polymer blended with polyethylene glycol (PEG) additive, and amine modified TiO2 by using phase inversion technique. Fourier transform infrared spectroscopy (FTIR), zeta potential (ζ), thermo gravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), water contact angle (WCA), and atomic absorption spectrophotometer (AAS) studies were done to characterize the membranes in terms of chemical structure, electric charge, thermal stability, morphology, hydrophilicity, and removal performance. The pure water permeability and Cr (VI) ion removal efficiency of the unmodified (i.e. CA/U-Ti) and the amine modified (CA/Ti-HMTA, CA/Ti-EDA, and CA/Ti-TEPA) membranes were dependent on pH and metal ion concentration. Incorporation of amine modified TiO2 composite to the CA polymer was found to improve the fouling and removal characteristics of the membranes during the chromium ultrafiltration process. The maximum removal efficiency result of Cr (VI) ions at pH of 3.5 using CA/Ti-TEPA membrane was 99.8%. The washing/regeneration cycle results in this study described as an essential part for prospect industrial applications of the prepared membranes. The maximum Cr (VI) removal results by using CA/Ti-TEPA membrane for four washing/regeneration cycles are 99.6%, 99.5%, 98.6% and, 96.6%, respectively.

Removal of bovine serum albumin from wastewater using fouling resistant ultrafiltration membranes based on the blends of cellulose acetate, and PVP-TiO2 nanoparticles.

Fouling resistant ultrafiltration membranes based on the blends of polyvinylpyrrolidone (PVP), TiO2 nanoparticles and cellulose acetate, CA-PVP-TiO2 (CATP), for removal of bovine serum albumin (BSA) were prepared by using phase inversion process. The influences of PVP and TiO2 on the preparation of phase inverted cellulose acetate (CA) ultrafiltration membrane were explored in terms of morphology study, equilibrium water content (EWC), hydraulic resistance, permeability performance, hydrophilicity, and thermal stability. After the introduction of PVP and TiO2 to the ternary (polymer-solvent-non-solvent) system, the formations of finger-like structures and macro-voids were reduced significantly. An improvement in porosity, average pore size, and hydrophilic nature of the CA membranes were detected after the introduction of PVP and TiO2 into the polymer matrix. The interaction between TiO2 and CA was confirmed and the degradation temperature of the CA membrane was significantly improved. BSA protein removal efficiency, anti-fouling performance, and recycling potential of the UF membranes were investigated. The CATP membrane (10.5 wt % CA: 4 wt % PVP: 2 wt % TiO2) has displayed high BSA removal efficiency and flux recovery ratios (NFR) with enhanced anti-fouling performances for the three fouling/rinsing cycles.