Sous Vide-Inspired Impregnation of Amorphous Titanium (Hydr)Oxide into Carbon Block Point-of-Use Filters for Arsenic Removal from Water.

Carbon block filters, commonly employed as point-of-use (POU) water treatment components, effectively eliminate pathogens and adsorb undesirable tastes, odors, and organic contaminants, all while producing no water waste. However, they lack the capability to remove arsenic. Enabling the carbon block to remove arsenic could reduce its exposure risks in tap water. Inspired by Sous vide cooking techniques, we developed a low-energy, low-chemical method for impregnating commercially available carbon block with titanium (hydr)oxide (THO) in four integrated steps: (1) vacuum removal of air from the carbon block, (2) impregnation with precursors in a flexible pouch, (3) sealing to prevent oxygen intrusion, and (4) heating in a water bath at 80 °C for 20 h to eliminate exposure and reactions with air. This process achieved a uniform 13 wt % Ti loading in the carbon block. Our modified carbon block POU filter efficiently removed both arsenate and arsenite from tap water matrices containing 10 or 100 µg/L arsenic concentrations in batch experiments or continuous flow operations. Surprisingly, the THO-modified carbon block removed arsenite better than arsenate. This innovative method, using 70% fewer chemicals than traditional autoclave techniques, offers a cost-effective solution to reduce exposure to arsenic and lower its overall risk in tap water.

Mechanistic Study of Arsenate Adsorption onto Different Amorphous Grades of Titanium (Hydr)Oxides Impregnated into a Point-of-Use Activated Carbon Block.

Millions of households still rely on drinking water from private wells or municipal systems with arsenic levels approaching or exceeding regulatory limits. Arsenic is a potent carcinogen, and there is no safe level of it in drinking water. Point-of-use (POU) treatment systems are a promising option to mitigate arsenic exposure. However, the most commonly used POU technology, an activated carbon block filter, is ineffective at removing arsenic. Our study aimed to explore the potential of impregnating carbon blocks with amorphous titanium (hydr)oxide (THO) to improve arsenic removal without introducing titanium (Ti) into the treated water. Four synthesis methods achieved 8-16 wt.% Ti loading within the carbon block with 58-97% amorphous THO content. The THO-modified carbon block could adsorb both oxidation states of arsenic (arsenate and arsenite) in batch or column tests. Modified carbon block with higher Ti and amorphous content always led to better arsenate removal, achieving arsenic loadings up to 31 mg As/mg Ti after 70,000 bed volumes in continuous flow tests. Impregnating carbon block with amorphous THO consistently outperformed impregnation using crystalline TiO2. The best-performing system (TTIP-EtOH carbon block) was an amorphous THO derived using titanium isopropoxide, ethanol, and acetic acid via sol-gel technique, aged at 80° for 18 hours and dried overnight at 60°. Comparable pore size distribution and surface area of the impregnated carbon blocks suggested that chemical properties play a more crucial role than physical and textural properties in removing arsenate via amorphous Ti-impregnated carbon block. Freundlich isotherms indicated energetically favorable adsorption for amorphous chemically synthesized adsorbents. The mass transport coefficients for the amorphous TTIP-EtOH carbon block were fitted using a pore surface diffusion model, resulting in Dsurface = 3.1×10-12 cm2/s and Dpore = 3.2×10-6 cm2/s. Impregnating the carbon block with THO enabled effective arsenic removal from water without adversely affecting the pressure drop across the unit or the carbon block's ability to remove polar organic chemical pollutants efficiently.

Direct Ink Writing of Metal Oxide/H-ZSM-5 Catalysts for n-Hexane Cracking: A New Method of Additive Manufacturing with High Metal Oxide Loading.

Previously, 3D printing of porous materials and metal oxides was limited to low loading metal loadings, as increasing the nitrate salt concentrations, which are used to generate the oxide component, gave rise to poor rheological properties beyond 10 wt %. In this study, we addressed this problem by directly printing insoluble oxides alongside H-ZSM-5 zeolite, which allowed for increased oxide loadings. Various metal oxides such as V2O5, ZrO2, Cr2O3, and Ga2O3 were doped onto H-ZSM-5 through the additive manufacturing method. Characterization and correlation between the X-ray diffraction, NH3-temperature-programmed desorption, O2-temperature programmed oxidation, temperature-programmed reduction, scanning electron microscopy-energy dispersive spectroscopy, and in situ CO2 DRIFTS experiments revealed that directly 3D printing metal oxides/H-ZSM-5 inks leads to significant modification in the surface properties and oxide bulk dispersion, thereby enhancing the composites' reducibility and giving rise to widely differing product distributions in n-hexane cracking reaction. The obtained metal oxide/zeolite structured materials were used as bifunctional structured catalysts for the selective formation of light olefins from hexane at 550-600 °C and GHSV = 9000 mL/gcatalst·h in a packed-bed reactor. Among the various compositions of metal oxides/H-ZSM-5 examined (i.e., 15 wt % Ga2O3, 15 wt % ZrO2, 15 wt % V2O5, 15 wt % Cr2O3, or 5 wt % Cr/10 wt % ZrO2/10 wt % V2O5/10 wt % Ga2O3 balanced with H-ZSM-5), the 15 wt % Cr/ZSM-5 monolith displayed the best n-hexane cracking performance, as it achieved 80-85% conversion of hexane with a 40% selectivity toward propylene, 30% selectivity toward ethylene, and 10% selectivity toward butene at 550 °C. The sample also showed zero benzene/toluene/xylene selectivity and no deactivation after 6 h. This study represents a proof-of-concept for tailoring customizable heterogeneous structured catalysts by directly 3D printing high loading of metal oxides/porous zeolite and is a breakthrough in material science.