Physicomechanical and Antimicrobial Characteristics of Cement Composites with Selected Nano-Sized Oxides and Binary Oxide Systems

In recent years, increasing attention has been paid to the durability of building materials, including those based on cementitious binders. Important aspects of durability include the increase of the strength of the cement matrix and enhancement of material resistance to external factors. The use of nanoadditives may be a way to meet these expectations. In the present study, zinc, titanium and copper oxides, used in single and binary systems (to better the effect of their performance), were applied as additives in cement mortars. In the first part of this work, an extensive physicochemical analysis of oxides was carried out, and in the second, their application ranges in cement mortars were determined. The subsequent analyses were employed in determining the physicochemical properties of pristine oxides: Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray fluorescence (EDXRF), scanning electron microscopy (SEM), measurement of the particle size distribution, as well as zeta potential measurement depending on the pH values. Influence on selected physicomechanical parameters of the cement matrix and resistance to the action of selected Gram-positive and Gram-negative bacteria and fungi were also examined. Our work indicated that all nanoadditives worsened the mechanical parameters of mortars during the first 3 days of hardening, while after 28 days, an improvement was achieved for zinc and titanium(IV) oxides. Binary systems and copper(II) oxide deteriorated in strength parameters throughout the test period. In contrast, copper(II) oxide showed the best antibacterial activity among all the tested oxide systems. Based on the inhibitory effect of the studied compounds, the following order of microbial susceptibility to inhibition of growth on cement mortars was established (from the most susceptible, to the most resistant): E. coli < S. aureus < C. albicans < B. cereus = P. aeruginosa < P. putida.

g-C3N4/MoS2 Heterojunction for Photocatalytic Removal of Phenol and Cr(VI)

In this study, molybdenum disulfide (MoS2) decorated on graphitic carbon nitride (g-C3N4) heterostructure catalysts at various weight ratios (0.5%, 1%, 3%, 10%, w/w) were successfully prepared via a two-step hydrothermal synthesis preparation method. The properties of the synthesized materials were studied by X-ray diffraction (XRD), attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FT-IR), UV–Vis diffuse reflection spectroscopy (DRS), scanning electron microscopy (SEM) and N2 porosimetry. MoS2 was successfully loaded on the g-C3N4 forming heterojunction composite materials. N2 porosimetry results showed mesoporous materials, with surface areas up to 93.7 m2g−1, while determined band gaps ranging between 1.31 and 2.66 eV showed absorption over a wide band of solar light. The photocatalytic performance was evaluated towards phenol oxidation and of Cr (VI) reduction in single and binary systems under simulated sunlight irradiation. The optimum mass loading ratio of MoS2 in g-C3N4 was 1%, showing higher photocatalytic activity under simulated solar light in comparison with bare g-C3N4 and MoS2 for both oxidation and reduction processes. Based on scavenging experiments a type-II photocatalytic mechanism is proposed. Finally, the catalysts presented satisfactory stability (7.8% loss) within three catalytic cycles. Such composite materials can receive further applications as well as energy conversion.

Removal of Toluidine Blue and Safranin O from Single and Binary Solutions Using Zeolite

The studies on dye removal from solutions attracted great attention due to the increased use of color dyes in different fields. However, most of the studies were focused on dye removal from a single solution. In reality, wastewater from the fabric industry could contain mixed dyes. As such, evaluating different dye removal from mixed solutions may have more practical importance. In terms of sorbents evaluated for dye removal, most of them were an organic type generated from agricultural wastes. Clay minerals and zeolites were also studied extensively, because of the vast reserves, inexpensive material cost, larger specific surface area (SSA) and high cation exchange capacity (CEC). However, evaluating the factors controlling the dye removal from mixed dye solutions was limited. In this study, the removal of cationic dyes safranin O (SO) and toluidine blue (TB) by clinoptilolite zeolite (ZEO) was evaluated under single and binary systems. The results showed that removal of TB was preferred over SO by approximately a 2:1 ratio. The counterion Cl− sorption from mixed dye solution helped the formation of mixed dye aggregates on mineral surfaces. Molecular dynamic simulation confirmed the multilayer mixed dye formation on ZEO under high loading levels.

Competitive Adsorption of Congo red in Single and Binary Systems Using a Low-cost Adsorbent

Background. Sawdust from Parkia biglobosa was prepared as an adsorbent for the adsorption of dye from aqueous solution. Objectives. The ability of sawdust to adsorb Congo red in a single dye system and binary dye system was examined. Methods. Effects of several variables (pH, contact time, initial dye concentration and adsorbent dose) were investigated and optimum conditions were established. The equilibrium data were subjected to kinetic and isotherm models. Results. Equilibrium time was observed at 600 mins while the optimum dose was 0.2 g and there was an increase in adsorption at low pH. The equilibrium data fitted the Freundlich isotherm model in both systems (coefficient correlation (R2) &gt; 0.9). Harkin-Jura was the worst-fitted (R2 &lt; 0.8). The qm in the single system (21.65) was lower than in BDS (27.17; 34.01). The values of 1/n show the heterogeneity on the surface of sawdust which reduced in the BDS. The increase in qm in the binary system showed that the presence of another dye (Reactive black 5) had a synergistic effect on the adsorption of Congo red. The kinetics of the process followed the pseudo-second-order model both in the single system and one of the binary systems. The dynamics of the process showed that the single system was non-spontaneous at low temperatures, endothermic and increased randomness on the surface of the adsorbent, while in the binary system, the process was exothermic and had little affinity for the adsorbent. Conclusions. Sawdust from Parkia biglobosa is a potential adsorbent for removing Congo red dye from aqueous solution in single and binary systems. Competing Interests. The authors declare no competing financial interests.

WO3 Fibers/g-C3N4 Z-Scheme Heterostructure Photocatalysts for Simultaneous Oxidation/Reduction of Phenol/Cr (VI) in Aquatic Media

A sequence of WO3/g-C3N4 composites was synthesized at various % weight ratios (1, 5, 6.5, 8, 10, and 15%) of WO3 into g-C3N4 via electrospinning and wet-mixing method. The prepared photocatalytic materials were characterized by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, UV–vis diffuse reflection spectroscopy (DRS), scanning electron microscopy (SEM), N2 porosimetry and dynamic light scattering (DLS). Electrospun fibers of WO3 with diameter 250–300 nm was prepared using polyvinylpyrrolidone (PVP) polymer and used for the synthesis of composite WO3/g-C3N4 heterojunction structures. Results showed mesoporous materials with triclinic WO3 crystal phase, surface areas up to 67.7 m2g−1 and band gaps lower than 2.5 eV confirming the absorption to visible light region. The photocatalytic performance of the prepared photocatalysts were assessed towards the oxidation of phenol and reduction of Cr (VI), in single and binary systems using simulated solar light illumination, that followed first-order kinetics. The WO3/g-C3N4 composites were found to exhibit improved photocatalytic performances compared to the pure WO3 and g-C3N4 with 6.5 wt% WO3/g-C3N4 and 5 wt% WO3/g-C3N4 composites being the most efficient catalysts for the oxidation of phenolics and reduction of Cr (VI), respectively. The improved performance was explained by a Z-scheme photocatalytic mechanism which was proposed based on scavenging experiments and the determination of the corresponding energy levels of valence and conduction bands. The study demonstrated that such composites present interesting photocatalytic properties that can be further expanded to other environmental depollution applications as well as in energy applications.