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Selective altering of surface wettability in microfluidic channels provides a suitable platform for a large range of processes, such as the phase separation of multiphase systems, synthesis of reaction controlled, nanoliter sized droplet reactors, and catalyst impregnation. Herein we study the feasibility to tune the wettability of a flexible cyclic olefin copolymer (COC). Two methods were considered for enhancing the surface hydrophilicity. The first is argon/oxygen plasma treatment, where the effect of treatment duration on water contact angle and COC surface morphology and chemistry were investigated, and the second is coating COC with GO dispersions of different concentrations. For enhancing the hydrophobicity of GO-coated COC surfaces, three reduction methods were considered: chemical reduction by Hydroiodic acid (HI), thermal reduction, and photo reduction by exposure of GO-coated COC to UV light. The results show that as the GO concentration and plasma treatment duration increased, a significant decrease in contact angle was observed, which confirmed the ability to enhance the wettability of the COC surface. The increase in hydrophilicity during plasma treatment was associated with the increase in surface roughness on the treated surfaces, while the increase during GO coating was associated with introducing oxygen-containing groups on the GO-coated COC surfaces. The results also show that the different reduction methods considered can increase the contact angle and improve the hydrophobicity of a GO-coated COC surface. It was found that the significant improvement in hydrophobicity was related to the reduction of oxygen-containing groups on the GO-coated COC modified surface.

Herein, we report the synthesis of hierarchical AlPO4-5 and SAPO-5 molecular sieves that exhibit varying degrees of mesoporous interconnectivity by controlling the amount of triethylamine (TEA) (used as the structure directing agent) and the Si-to-Al ratio (Si/Al); the gel mixture had a composition of (1 − y) Al2O3:y SiO2:1.3 P2O5:x TEA:200 H2O. The molecular sieves were characterized by X-Ray powder Diffraction (XRD) and Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM/EDX), and their sorption properties were studied by N2 adsorption-desorption at 77 K and water adsorption at 316 K. In the synthesis gel with x = 1.6 ((1 − y) Al2O3:y SiO2:1.3 P2O5:1.6 TEA:200 H2O), SAPO-5 and AlPO4-5 exhibit high Brunauer-Emmett-Teller specific surface areas of ~380 m2 g−1 and 325 m2 g−1, respectively. SAPO-5, having a composition of Si0.46Al0.6P0.804, exhibits significant water uptake at low relative pressures (3.4 mmol/g at P/P0 = 0.03 vs. 0.2 mmol/g for pure AlPO4-5) attributed to the contribution of hydrophilic Bronsted acid sites, arising from the charge imbalance created by the isomorphic substitution of Si into the aluminophosphate structure predominantly via the SM2 mechanism. Furthermore, SAPO-5 exhibited a hierarchical pore structure having distinct pore size distributions centred on 0.7 nm and 15.8 nm, attributed to the AFI framework and the induced mesoporosity, respectively. At higher relative pressures, SAPO-5 exhibited the highest total water adsorption capacity of 14.1 mmol/g at a relative pressure of 0.38, compared to 11 mmol/g for AlPO4-5. The higher overall capacity of SAPO-5 is attributed to capillary condensation into the relatively large mesopore volume.

Metal substitution in aluminophosphates is known to induce unique structural and surface characteristics that can tune catalytic performance. Si, Co, Fe and Mg substituted AlPO4-5 (MeAPO-5) catalysts were hydrothermally prepared, characterized, and evaluated for ethanol - acetic acid esterification. Textural evaluation revealed that the Co and Si analogues possessed an order of magnitude higher mesopore volume compared to the rest of the studied materials. Divalent metal ions (i.e. Co, Fe, and Mg) substituted preferentially Al ions via the SM1 mechanism, as confirmed by the P/Al being greater than one, while Si ions substituted P ions (SM2) initially, followed by substitution of pairs of Al-P ions (SM3) at higher Si content. The esterification catalytic activity was found to follow the order SAPO-5 > > CoAPO-5 > MgAPO-5 ≈ FeAPO-5. The superior performance of SAPO-5 is ascribed to the higher concentration of Bronsted acid sites and faster mass transfer rates due to the relatively small crystal size and larger fraction of mesopores. Notably, the SAPO-5 with the optimal Si content demonstrated comparable stability against deactivation within the range of reaction conditions studied and sustained catalytic activity at prolonged reaction durations when compared to commercial Zeolite β, despite the significantly higher surface area, pore volume and density of acid sites of the latter, primarily attributed to less strong adsorption of the reaction products. The reported parametric results for various metal substitutions shed light towards optimizing aluminophosphate catalysts for esterification applications.

Isomorphic substitution of zeolite and zeotype materials can affect significantly their application performance. The work presented herein assesses the impact of cobalt and silicon substitution at low and high H2O/Al2O3 of the reaction mixture by a combination of experimental and density functional theory (DFT) calculations. The presence of cobalt in the synthesis mixture promotes the formation of large single columnar crystals exhibiting dominant growth along the c- (out-of-plane) axis. In dense reaction mixtures (H2O/Al2O3 molar ratio of 100), the promotional effect of cobalt is counteracted by the effect of the low water content which alters crystal morphology. For cobalt substituted AlPO4-5, the unit cell experiences contraction or expansion when Co substitutes Al or P, respectively. The lack of stability at higher cobalt content is attributed to the introduction of structural defects upon Co+2 incorporation. The presence of silicon promotes the formation of intergrown crystals at all conditions. At dilute reaction mixtures (H2O/Al2O3 ratio of 400), the presence of silicon promotes growth in all directions especially along the out-of-plane axis. At H2O/Al2O3 of 100, the presence of silicon promotes in-plane growth. Lattice refinement results do not show a clear correlation between Si/Al2O3, H2O/Al2O3 and the lattice parameters. DFT analysis suggest that the unit cell experiences a contraction when: 1) Si substitutes Al-P pairs and 2) Si substitutes one P in two unit cells. An expansion in the unit cell occurs when Si replaces P in one unit cell. The results also suggest the absence of preferred substitution mode for Si (i.e. either P or Al-P pairs).