Publications

Global water quality has deteriorated, leaving over 844 million individuals without access to clean drinking water. While sand filters (SF) offer a solution, their limited surface area and adsorption capacity for emerging contaminants remain a challenge. This has prompted the development of new materials such as graphene-coated sand (GCS) to enhance the sand's adsorptive properties. Notably, GCS also possesses inherent anti-bacterial properties and can function as a photocatalyst when exposed to UV and visible light, offering enhanced water purification. This manuscript 1) reviews the synthesis of GCS, detailing the characterization techniques employed to understand its structure, composition, and multifunctional properties and 2) highlights the superior efficacy of GCS in removing contaminants, including metals (>95 % removal of Cd²⁺, Pb²⁺, Zn²⁺, and Cu²⁺ in low pH environment), sulfides (full removal compared to 26 % removal by raw sand), antibiotics (98 % removal of tetracycline), and bacteria (complete cell membrane destruction), compared to traditional SF. Due to its enhanced performance and multifaceted purification capabilities, GCS presents a promising alternative to SFs, especially in developing countries, aiming to improve water quality and ensure safe drinking water access. To the best of our knowledge, no other work groups the available research on GCS. Furthermore, future research directions should focus on reducing the overall production cost of GCS, exploring surface modification techniques, and expanding the range of contaminants tested by GCS, to fully realize its potential in water purification.

Optimized extrusion melt-blending of polylactic acid (PLA) polymer with a minor biopolymeric phase, polybutylene adipate terephthalate (PBAT), and compatibilized with random ethylene-methyl acrylate-glycidyl methacrylate terpolymer (EMA-GMA, Trademark: Lotader AX-8900) led to an outstanding improvement in mechanical properties. At the noncompatibilized PLA–PBAT (80–20) blend point, significant enhancement (∼4500%) in toughness and elongation-at-break was already obtained without compromising any elastic properties. The effect of the compatibilizer content on the mechanical properties of the PLA–PBAT (80–20) blend was investigated by an optimal custom response surface methodology. Thus, 2 wt % Lotader content was determined to be optimal by a numerical optimization methodology with a desirability value, D, of 0.882 to maximize toughness and elongation-at-break. The compatibilization and thermal behavior of the Lotader-modified blends were analyzed by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Upon adding the compatibilizer, the original phase-separated morphology of the blends changed from PBAT quasi-spherical domains to nearly elongated elliptical ones. It was also found that the interfacial boundary line of the domains faded away, which revealed that interfacial compatibility was achieved. The thermostability of the blends remained largely unaltered following the incorporation of PBAT and Lotader. Moreover, while PBAT exhibited a minor influence on the crystallinity of PLA, Lotader had no discernible impact on crystallinity, as evidenced by the DSC thermograms. Thus, the compatibilizer at the optimal point in the optimized blend ratio led to the formation of a phase-separated morphology that combined internal cavitation, interfacial cavitation, and strong adhesion features at the right proportions in the microstructure which underlies the micromechanisms driving the remarkable enhancement of as much as 7100% in toughness and ductility.

This paper presents a numerical study on the dynamic response and impact mitigation capabilities of layered ceramic–polymer–metal (CPM) composites under plate impact loading, focusing on the layer sequence effect. The layered structure, comprising a ceramic for hardness and thermal resistance, a polymer for energy absorption, and a metal for strength and ductility, is analyzed to evaluate its effectiveness in mitigating the impact loading. The simulations employed the VUMAT subroutine of DSGZ material models within Abaqus/Explicit to accurately represent the mechanical behavior of the polymeric materials in the composites. The VUMAT implementation incorporates the explicit time integration scheme and the implicit radial return mapping algorithm. A safe-version Newton–Raphson method is applied for numerically solving the differential equations of the 𝐽2 plastic flow theory. Analysis of the simulation results reveals that specific layer configurations significantly influence wave propagation, leading to variations in energy absorption and stress distribution within the material. Notably, certain layer sequences, such as P-C-M and C-P-M, exhibit enhanced impact mitigation with a superior ability to dissipate and redirect the impact energy. This phenomenon is tied to the interactions between the material properties of the ceramic, polymer, and metal, emphasizing the necessity of precise material characterization and enhanced understanding of the layer sequencing effect for optimizing composite designs for impact mitigation. The integration of empirical data with simulation methods provides a comprehensive framework for optimizing composite designs in high-impact scenarios. In the general fields of materials science and impact engineering, the current research offers some guidance for practical applications, underscoring the need for detailed simulations to capture the high-strain-rate dynamic responses of multilayered composites.

In this work, an I-optimal response surface model was used to systematically investigate the effects of graphene (Gr) content (Factor A; 0–10 wt%), temperature (Factor B; 0–200°C), and Gr layer structure (Factor C; monolayer versus five-layer) on the thermal conductivities of PEI/Gr nanocomposites, which were determined using reverse non-equilibrium molecular dynamics (RNEMD) simulation with the Müller-Plathe algorithm. Based on a reduced quadratic model that was fit to the data, the effect of Factor A on thermal conductivity was found to be more pronounced for the PEI/Gr nanocomposite with the five-layer Gr structure. Moreover, Factor B had expectedly the largest effect on thermal conductivity, followed by Factor C. However, these two factors were involved in significant interactions with Factor A. Based on numerical optimizations, the predicted thermal conductivities of the PEI/Gr nanocomposites varied from 0.057 (minimum) to 0.174 W m⁻¹ K⁻¹ (maximum). Overall, the maximum thermal conductivity of the PEI/Gr nanocomposite may be obtained at any given temperature in the range of 0–200°C by the addition of multi-layer Gr (a cheaper alternative to monolayer Gr) at a content of 10 wt%. For example, the addition of 10 wt% five-layer Gr to PEI at room temperature (25°) results yields an increase in its thermal conductivity of about 30%. Also, going from 0 to 100°C, an increase of about 76% is predicted for the thermal conductivity of the PEI/Gr nanocomposite containing 10 wt% five-layer Gr. The results of this study shed light on the interactions between the three investigated factors.

Herein, the development of new nanocomposite systems is reported based on one-part polyurea (PU) and aminopropyl isobutyl polyhedral oligomeric silsesquioxane (POSS)-functionalized graphene nanoplatelets (GNP-POSS) as compatible nanoreinforcements with the PU resin. GNP-POSS was effectively synthesized via a two-step synthesis protocol, including ultrasonication-assisted reaction and precipitation, and carefully characterized with respect to its chemical and crystalline structure, morphology, and thermal stability. FTIR and XPS spectroscopy analyses revealed that POSS interacts with the residual oxygen moieties of the GNPs through both covalent and noncovalent bonding. The X-ray diffraction pattern of GNP-POSS further revealed that the crystallinity of the GNPs was not altered after their functionalization with POSS. GNP-POSS was successfully incorporated in PU at contents of 1, 3, 5, and 10 wt % to yield PU/GNP-POSS nanocomposite films. An ATR-FTIR analysis of these films confirmed the presence of strong interfacial interactions between the urea groups of PU and the GNP-POSS functionalities. Moreover, the PU/GNP-POSS nanocomposite films exhibited enhanced thermal stability and mechanical properties compared to those of the neat PU film. The quasi-static tensile testing of the PU/GNP-POSS samples revealed remarkable enhancements in the tensile strength (from 7.9 for the neat PU to 25.1 MPa for PU/GNP-POSS) and Young’s modulus (238–617 MPa), while elongation at break and toughness also showed 14 and 125% improvements, respectively. Finally, the effects of GNP-POSS content on the morphological, quasistatic tensile, and high-strain-rate dynamic behavior of the PU/GNP-POSS nanocomposite films were also investigated. Overall, the tests performed using a split-Hopkinson pressure bar setup revealed a large increase in the film strength (from 147.6 for the neat PU film to 199 MPa for the PU/GNP-POSS film) and a marginal increase in the energy density of the film (38.1–40.8 kJ/m³). These findings support the suitability of the PU/GNP-POSS nanocomposite films for force protection applications.

Poly(vinyl alcohol) (PVA)/graphene nanoplatelet (GnP) nanocomposite films were fabricated by a solution casting method. High loadings (30–40 wt.%) of two GnP grades, that is, xGnP C300 (low surface area/large size) and C750 (high surface area/small size), were utilized in combination with three commercial dispersing agents, that is, DISPERBYK-161, DISPERBYK-162 TF, and DISPERBYK-2014, to yield films with desirable stiffness and energy dissipation characteristics (dynamic mechanical analysis, DMA), as well as thermal properties (thermogravimetric analysis, TGA) for potential impact resistance applications. The addition of GnPs and dispersing agents to PVA leads to a maximum six-fold increase in its Young's modulus for the PVA sample containing 40 wt.% C300 GnPs and DISPERBYK-162 TF. However, the modulus of resilience drops dramatically for the same sample (about 18-fold decrease), as expected. Also, C300 GnPs yield nanocomposites with higher Young's moduli that those obtained using C750 GnPs. The atomic force microscopy stiffness maps illustrate that C300 GnPs disperse better in the PVA matrix. Furthermore, the average interphase thickness in the PVA-C300 nanocomposites (~300 nm) is almost double that of PVA-C750 nanocomposites. Based on the TGA results, the addition of GnPs and dispersing agent to the PVA matrix leads to a moderate increase (an average of 3.5%) in the T_max value of the neat PVA, while its char yield increases by an average 8.5-fold. Specifically, the PVA/GnP nanocomposites containing DISPERBYK-162 TF yield the largest T_max and char yield values than the other systems. The insights gained in this work can guide the design of coatings for impact resistance applications.

Graphene oxide (GO) and its derivatives find application in fields such as biomedicine, electronics, energy, and the environment. They also play a significant role in the modification of infrastructure materials, such as asphalt and cement. In this study, we oxidized commercially available graphite (Gr) powder and graphene nanoplatelets (GNPs) using an improved Hummers’ method. We first investigated the effects of particle sizes and specific surface areas of the Gr and GNP precursors on their oxidation, which have not been addressed in literature. The results from Fourier transform infrared and X-ray photoelectron spectroscopy analyses show that oxidized Gr (designated ox-Gr or simply GO) with a large surface area and small particle size has a higher degree of oxidation than that of oxidized GNPs (designated oxidized multilayer graphene) with about 9.8% carboxyl functional groups that provide favorable interactions with asphalt binder components. Next, we investigated the effect of this carboxyl-rich GO on the high-temperature performance of the asphalt binder through rotational viscosity, rheology, multiple stress creep and recovery (MSCR), and antiaging property measurements. Our results indicate that the introduction of only 2 wt % GO to a performance-grade asphalt binder (PG 67–22) can dramatically increase its complex shear modulus (G*), as well as decrease the phase angle (δ), at high temperatures. The MSCR tests show that the addition of GO to the asphalt binder effectively mitigates its permanent deformation and improves its elastic response, as demonstrated by a reduction of about 39% in the creep compliance (J_nr) and an impressive 297% increase in the percent recovery (εR) of the GO-modified binder. Furthermore, the measured viscosity aging index and G* ratio of the GO-modified asphalt binder confirm the significant effect of GO on the improvement of the antiaging properties of the binder.

Since their emergence in 2014, graphitic carbon nitride quantum dots (g-C₃N₄ QDs) have attracted much interest from the scientific community due to their distinctive physicochemical features, including structural, morphological, electrochemical, and optoelectronic properties. Owing to their desirable characteristics, such as non-zero band gap, ability to be chemically functionalized or doped, possessing tunable properties, outstanding dispersibility in different media, and biocompatibility, g-C₃N₄ QDs have shown promise for photocatalysis, energy devices, sensing, bioimaging, solar cells, optoelectronics, among other applications. As these fields are rapidly evolving, it is very strenuous to pinpoint the emerging challenges of the g-C₃N₄ QDs development and application during the last decade, mainly due to the lack of critical reviews of the innovations in the g-C₃N₄ QDs synthesis pathways and domains of application. Herein, an extensive survey is conducted on the g-C₃N₄ QDs synthesis, characterization, and applications. Scenarios for the future development of g-C₃N₄QDs and their potential applications are highlighted and discussed in detail. The provided critical section suggests a myriad of opportunities for g-C₃N₄ QDs, especially for their synthesis and functionalization, where a combination of eco-friendly/single step synthesis and chemical modification may be used to prepare g-C₃N₄ QDs with, for example, enhanced photoluminescence and production yields.

This paper investigates the potential of graphene-coated sand (GCS) as an advanced filtration medium for improving water quality and mitigating chemicals of emerging concern (CECs) in treated municipal wastewater, aiming to enhance water reuse. The study utilizes three types of sand (Ottawa, masonry, and concrete) coated with graphene to assess the impact of surface morphology, particle shape, and chemical composition on coating and filtration efficiency. Additionally, sand coated with graphene and activated graphene coated sand were both tested to understand the effect of coating and activation on the filtration process. The materials were characterized using digital microscopy, Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction analysis. The material's efficiency in removing turbidity, nutrients, chemical oxygen demand (COD), bacteria, and specific CECs (Aciclovir, Diatrizoic acid, Levodopa, Miconazole, Carbamazepine, Diphenhydramine, Irbesartan, Lidocaine, Losartan, and Sulfamethoxazole) was studied. Our findings indicate that GCS significantly improves water quality parameters, with notable efficiency in removing turbidity, COD (14.1 % and 69.1 % removal), and bacterial contaminants (64.9 % and 99.9 % removal). The study also highlights the material's capacity to remove challenging CECs like Sulfamethoxazole (up to 80 % removal) and Diphenhydramine (up to 90 % removal), showcasing its potential as a sustainable solution for water reuse applications. This research contributes to the field by providing a comprehensive evaluation of GCS in water treatment, suggesting its potential for removing CECs from treated municipal wastewater.

The feasibility of carbon nanofibers (CNF) to impart transport properties to a flexible and ductile polyethylene matrix for electromagnetic compatibility (EMC) was assessed in contrast to traditional carbon fibers (CF). Raman spectroscopy and electrical resistivity measurements of the bulk of the carbon fillers showed that commercial Pyrograf-III, PR-19 grade CNF were significantly more amorphous with lower transport properties than Thornel P-55 CF. A range of CNF/polyethylene nanocomposites (concentrations 0–40 wt %) were prepared via twin-screw extrusion and their electrical, dielectric, electrostatic dissipation, electromagnetic shielding, and mechanical properties were investigated. Good dispersion was revealed by electron microscopy, demonstrating the dispersibility of CNFs. PR-19 CNF led to superior surface conductivity and electrostatic dissipation at low concentrations. Nevertheless, the microcomposites prepared with P-55 pitch-based CF led to higher electromagnetic shielding (∼11 dB), electrical conductivities (i.e., surface resistivity of 1.4 × 10³ Ω/sq), and relative permittivity (72.2–81.5j) at larger concentrations, displaying an in-plane anisotropic behavior. The microcomposites, though, displayed a stiff (modulus ∼1.4 GPa at 40 wt %), weak (breaking strength of only ∼3 MPa at 40 wt %), and brittle behavior (<3% at 40 wt %), whereas the nanocomposites retained acceptable flexibility (modulus ∼1 GPa), strength (∼10 MPa), and ductility (∼30%) at comparable concentrations. This study points out the feasibility of pristine CNFs for flexible thin-wall materials for EMC applications.