Synthesis and properties of polydimethylsiloxane/graphene oxide modified,water-based polyurethane/polyacrylate

In this study, we prepared polydimethylsiloxane–graphene oxide (PG) modified waterborne polyurethane acrylate (WPUA) films and enhanced their hydrophobicity, thermal stability, and mechanical properties. The prepared films were characterized by Fourier transform infrared and energy spectroscopy analysis; this confirmed the successful incorporation of PG into WPUA. As shown by scanning electron microscopy and atomic force microscopy analysis, the surfaces of the WPUA films were confirmed to have turned smoother and more compact after PG addition. With an optimized amount of PG (0.1%) incorporated into the WPUA film, it exhibited a contact angle improvement of 21.9°, an enhanced decomposition temperature at 5% weight losses of 25 °C, and an elongation at break improvement of 482.92% over those of pure WPUA. The newly synthesized PG–WPUA showed considerable enhancements in its hydrophobicity and thermal and mechanical properties and could be deemed to have potential value as an alternative contender for practical applications in coatings painted on tunnels and highways. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47926.     

Surface and bulk properties of waterborne polyurethane modified with fluorinated siloxane

Two series of polyester and polyether waterborne polyurethanes (WPUs) modified with poly[(3,3,3‐trifluoropropyl)methylsiloxane] (PTFPMS) were synthesized by prepolymerization method and the effect of PTFPMS on surface and bulk properties were investigated by a variety of experimental methods. FTIR and DSC results showed that the polyester WPU has better compatibility between soft segments and hard segments than polyether WPU in bulk and the degree of phase separation increased in polyester WPU but decreased in polyether WPU with increasing PTFPMS. ARXPS analysis revealed the migration of PTFPMS to WPU surface and the migration ability of Si element was better than F element. AFM images demonstrated that the surface of WPU films became rougher as PTFPMS content increased. The enrichment of PTFPMS with low surface energy and roughened surface imparted good hydrophobicity and oleophobicity to WPU films and polyether WPU has better surface properties compared with polyester WPU. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46473.     

Influence of surface properties on the dip coating behavior of hollow fiber membranes

Coating processes have become an important fabrication step in membrane production, either to form a separation layer on a porous substrate or to tune specific properties. The coating procedure depends to a large extent on the membrane properties which substantially impedes a prediction of the coating thickness. To give an insight into the coating properties of various hollow fiber membranes, a selection of membranes with different pore sizes was coated with aqueous poly(vinyl alcohol) solutions at various coating velocities. It was found that material properties and pore sizes of the membranes have great influence on coating thicknesses. An intrusion of coating material into the membrane structure was determined with increasing pore size. Pure intrusion without formation of a dense surface layer took place when using a membrane with a mean pore size of ca. 500 nm. Coating results were correlated with the theoretical LLD law and for some membranes the coating thickness can be predicted quite well by the LLD law and its enhancements. When a significant amount of coating material penetrated into the membrane structure the LLD law loses its validity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46163.     

Bulk and surface mechanical properties of clay modified HDPE used in liner applications

High‐density polyethylene (HDPE)/clay nanocomposites were prepared by melt blending process. The HDPE was mixed with different organoclays and polyethylene‐grafted‐maleic anhydride was used as a compatibiliser. A masterbatch procedure was used to obtain final organoclays concentrations of 1, 2.5 and 5 wt%. The effects of various types of nanoclays and their concentrations on morphological, thermal and mechanical properties of nanocomposites were investigated. Surface mechanical properties such as instrumented nanohardness, modulus of elasticity and creep were also measured using a nanoindentation technique. Young's, storage and loss moduli, were found to be higher than that of the neat polymer at low loading (2.5 wt%) for clay Cloisite 15A and at higher loading (5 wt%) for clay Nanomer 1.44P. The ultimate strength and the toughness decreased slightly compared to pure HDPE. The differential scanning calorimetry analysis revealed that the peak temperature of the nanocomposites increased with increased clay content while the crystallinity decreased. Also, dynamic mechanical analysis revealed the storage and loss moduli are enhanced by addition of nanoclay. Both mechanical and thermal properties of HDPE/Nanomer 1.44P nanocomposite showed interesting trends. All properties first dropped when 1 wt% of the clay was added. Thereafter, a gradual increase or decrease then followed as the loading of Nanomer was increased. These trends were observed for all mechanical properties. The results obtained from nanoindentation tests for surface mechanical properties also showed similar trend to that of bulk measurements. Based on these measurements a nanoclay additive for a liner grade HDPE was selected. © 2011 Canadian Society for Chemical Engineering     

Influence of nanoparticles and antioxidants on mechanical properties of titania/polydicyclopentadiene polyHIPEs: A statistical approach

Open porous Pickering poly(high internal phase emulsion) composites were prepared by ring opening metathesis polymerization of surface modified TiO₂ nanoparticle stabilized dicyclopentadiene (DCPD) high internal phase emulsions. Oxidation of the double bonds in the polyDCPD chains of the resulting materials was prevented using antioxidants. Oxidation dependent variation of mechanical properties was demonstrated by applying compression tests to the resulting composite materials periodically. Periodical measurements revealed significantly reduced brittleness in the case of antioxidant containing polyHIPE composites. Furthermore, it was determined that the initial compression moduli and the compressive strengths of the resulting materials were significantly improved by using antioxidants as compared to antioxidant free samples. Moreover, increasing nanoparticle amount was found to have a beneficial effect with the presence of antioxidants. The relationship between the compression modulus with nanoparticle loading and different types of antioxidants was revealed by developing model regression equations and graphs. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46913.     

Evaluation of mechanical properties and hydrophobicity of room-temperature,moisture-curable polysilazane coatings

Polysilazane coatings have a broad need in real-life applications, which require low processing or working temperature. In this work, five commercially available polysilazanes have been spin-coated on polycarbonate substrates and cured in ambient environment and temperature to obtain transparent, crack-free, and dense films. The degree of crosslinking is found to have a significant impact on the hardness and Young's modulus of the polysilazane films but has a minor influence on the film thickness and hydrophobicity. Among all five polysilazane coatings, the inorganic perhydropolysilazane-based coating exhibits the largest hardness (2.05 ± 0.01 GPa) and Young's modulus (10.76 ± 0.03 GPa) after 7 days of curing, while the polyorganosilazane-derived films exhibit higher hydrophobicity. The molecular structure of polysilazanes plays a key role in mechanical properties and hydrophobicity of the associated films, as well as the adhesion of coatings to substrates, providing an intuitive and reliable way for selecting a suitable polysilazane coating material for a specific application.     

Synthesis and characterization of eugenol-based silicone modified waterborne polyurethane with excellent properties

A eugenol-based silicone-containing monomer 4,4′-(1,1,3,3-tetramethyldisiloxane-1,3-dipropyl)bis-2-methoxyphenol(EUSi) was synthesized from eugenol and 1,1,3,3-tetramethyldisiloxane via the hydrosilylation reaction. And waterborne polyurethane (WPU) with excellent properties was obtained by using EUSi as a type of diol chain extender. The unique combination of rigidity and flexibility in the chemical structure of EUSi greatly facilitated the mechanical properties, thermal properties, and water resistance of WPU. With only a 3% dosage of EUSi, the maximum tensile strength was increased from 6.2 to 22.4 MPa, while the water absorption was decreased from 31.3% to a surprisingly 7.6%. Our work provides a new convenient strategy for the preparation of organosilicon-modified WPU with improved performance.     

Molecular dynamics simulation on interacting and mechanical properties of polylactic acid and attapulgite(100) surface

The method of molecular dynamics (MD) simulations was used to investigate the interaction between the PLA and the attapulgite, and the influence of the temperature on the mechanical properties of the PLA and the PLA‐attapulgite. After the PLA blends the attapulgite, the structures and properties of the PLA and the attapulgite change due to their strong interaction. However, this interaction weakens gradually with temperature increasing. The isotropy of the composite of PLA‐attapulgite is strengthened in comparison with the PLA. In addition, the temperature can change the mechanical properties of the PLA‐attapulgite, but the mechanical properties of the PLA are hardly influences on the temperature. The PLA‐attapulgite is more rigid and tough than the PLA at the room temperature but the toughness of the composite of PLA‐attapulgite becomes worse than that of the PLA at 350 K. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Morphological effects of spherical SiO2 and hexagonal mesoporous MCM-41 nanoparticles in polyacrylonitrile mixed matrix membranes on the biofouling mitigation in short-term filtration

In this study, the morphology of the nanostructures is evaluated on the surface characterization and performance of the polyacrylonitrile (PAN) ultrafiltration mixed matrix membranes (MMM). To this end, silica nanoparticles (NPs) such as spherical (SiO₂) and hexagonal mesoporous (MCM-41) with high hydrophilicity were incorporated at 0.5, 1, and 2 wt%. Attenuated total reflectance-Fourier transform infrared analysis illustrated the placement of NP on the surface of the MMM. Atomic force microscopy studies also showed that SiO₂ NP added to PAN exhibited a smoother surface than MCM-41 NP. Field-emission scanning electron microscope analysis of the MMM identified that all membranes are composed of a finger-like porous structure. Contact angle measurements indicate that the morphology of the NPs has no significant effect on MMM hydrophilicity. Moreover, the performance of the MMM was evaluated, and regardless of NP morphology, the MMM showed better permeate flux with increased loading. A higher pure water flux was observed in the PAN-MCM41-1% membrane (237 L/m² h), possibly because of inherent porosity and high hydrophilicity of MCM-41 compared to SiO₂ NP. Further, the PAN-SiO₂-1% membrane exhibited superior antifouling properties due to a lower surface roughness. The present studies reveal that the morphology of the NP greatly influence on the structure, permeation, and antifouling properties of PAN membranes.     

Thermal and mechanical properties of epoxy resin reinforced with modified iron oxide nanoparticles

Epoxy polymers, having good mechanical properties and thermal stability, are often used for engineering applications. Their properties can be further enhanced by the addition of iron oxide (Fe₃O₄) nanoparticles (NPs) as fillers to the resin. In this study, pristine Fe₃O₄ NPs were functionalized with polydopamine (PDA), (3-glycidoxypropyl)trimethoxysilane (GPTMS), and (3-aminopropyl)trimethoxysilane (APTES). X-ray diffraction and scanning electron microscopy (SEM) were used to study any changes in the crystal structure and size of the NPs while Fourier-Transform Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA) were used to ensure the presence of functional groups on the surface. The mechanical properties of the Fe₃O₄-based nanocomposites generally improved except when reinforced with Fe₃O₄/PDA. The maximum improvement in tensile strength (∼34%) and fracture toughness (∼13%) were observed for pristine Fe₃O₄-based nanocomposites. Dynamic mechanical analysis (DMA) showed that the use of any of the treated NPs improved the material's initial storage modulus and had a substantial impact on its dissipation potential. Also, it was observed that the glass transition temperature measurements by DMA and differential scanning calorimetry were below that of pure epoxy. SEM of the cracked surfaces shows that the incorporation of any NPs leads to an enhancement in its thermal and mechanical properties.     

Cryogenic mechanical properties and failure mechanism of epoxy nanocomposites modified by multiwalled carbon nanotubes with tunable oxygen-containing groups on surface

The surface chemistry and structure of multiwalled carbon nanotube (MWCNT) plays an important role in MWCNT/epoxy nanocomposites. In this contribution, oxidized multiwalled carbon nanotube (OMCNT) with tunable oxygen-containing groups is prepared by finely controlling oxidation time and centrifugal speeds. Effects of oxygen-containing group content on mechanical properties of the OMCNT/E51 epoxy nanocomposites at 77 K are investigated in detail. It reveals that oxygen-containing groups on the OMCNT surface contribute to significant increases in tensile strength and impact resistance of the OMCNT/E51 epoxy nanocomposites compared with those of the pristine MWCNT/E51 nanocomposites. A positive correlation between the oxygen-containing group content and interfacial properties of OMCNT and epoxy matrix is demonstrated by thermogravimetric analysis and fracture morphology, and homogeneous dispersion of the OMCNT in epoxy matrix is obtained with the increase of oxygen-containing groups on surface of the OMCNT. However, proper content of oxygen-containing groups is essential to OMCNT/E51 nanocomposites because excessive oxidation tends to make sever structural defects on the OMCNT and has a side effect on cryogenic mechanical properties of OMCNT/E51 nanocomposites.     

Influence of ZnO nanoparticles on the cure characteristics and mechanical properties of carboxylated nitrile rubber

Zinc oxide (ZnO) nanoparticles assembled in one dimension to give rod‐shaped morphology were synthesized. The effect of these ZnO nanoparticles (average particle size ～ 50 nm) as the curing agent for carboxylated nitrile rubber was studied with special attention to cure characteristics, mechanical properties, dynamic mechanical properties, and swelling. These results were compared with those of the conventional rubber grade ZnO. The study confirmed that the ZnO nanoparticles gave a better state of cure and higher maximum torque with a marginal decrease in optimum cure time and scorch time. The mechanical properties also showed an improvement. There was an increase in tensile strength by ～ 120%, elongation at break by ～ 20%, and modulus at 300% elongation by ～ 30% for the vulcanizate cured with ZnO nanoparticles, as compared with the one containing rubber grade ZnO. Dynamic mechanical analysis revealed that the vulcanizates exhibited two transitions—one occurring at lower temperature due to the T_g of the polymer, while the second at higher temperature corresponding to the hard phase arising due to the ionic structures. The second transition showed a peak broadening because of an increase in the points of interaction of ZnO nanoparticles with the matrix. The tan δ peak showed a shift towards higher T_g in the case of ZnO nanoparticle‐cured vulcanizate, indicating higher crosslinking density. This was further confirmed by volume fraction of rubber in the swollen gel and infrared spectroscopic studies. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and properties of modified graphene oxide incorporated waterborne polyurethane acrylate

In this study, a new modifier (KPG) was prepared by modifying graphene oxide with γ‐glycidoxypropyl trimethoxysilane (KH560) and polydimethylsiloxane (PDMS). KPG was in turn added to aqueous urethane acrylate for the fabrication of waterborne polyurethane polyacrylate emulsion modified with KH560‐PDMS composite (KPG/WPUA). Textural characterizations of the KPG/WPUA coating were achieved via Fourier transform infrared, SEM, TGA and AFM techniques, which revealed that the KPG/WPUA film possessed a smooth surface. The synthesized KPG/WPUA films were tested for mechanical properties, hydrophobicity and acid/water corrosion performance which suggested their highly hydrophobic surface. KPG/WPUA with 0.1% KPG showed a contact angle of 118.35°, 30.35° higher than that of pristine WPUA. The KPG/WPUA film exhibited higher thermal stability, i.e. a 5% weight loss temperature of 305 °C, which was 30 °C higher than that of pristine WPUA film. The Young's modulus and elongation at break of the KPG/WPUA film were 34.1 MPa and 74.88% respectively, which were higher than that of WPUA film. Furthermore, KPG/WPUA films exhibited greater resistance (without obvious blistering and the white spotting phenomenon) to H₂O₂, HCl and water corrosion than pristine WPUA. The superior performance of KPG/WPUA films was attributed to the network chain structure formed upon the introduction of KPG into WPUA. The outstanding performance of KPG/WPUA films in terms of mechanical properties, thermal stability and high resistance to acidic and water corrosion makes them interesting alternative contenders for target applications. © 2019 Society of Chemical Industry     

The effects of modified zinc oxide nanoparticles on the mechanical/thermal properties of epoxy resin

Characterized by its strength, durability, and thermal properties, epoxy resin has been widely used as an adhesive, paint, and coating in many applications in the aerospace, civil and automotive industries. Despite this, the thermoset polymer resin has been known for its brittleness and low fracture resistance. This study focuses on the reinforcement of an epoxy resin system (diglycidyl ether of bisphenol A) with zinc oxide (ZnO) nanoparticles in their pristine form and a further modified form. The modification took place in two ways: coating with polydopamine (PDA) and covalently functionalizing them with (3-aminopropyl)triethoxysilane (APTES) and (3-glycidoxypropyl)trimethoxysilane (GPTMS). Therefore, four different types of nanoparticles were used: pristine ZnO, ZnO/PDA, ZnO/GPTMS, and ZnO/APTES aiming to improve the interfacial bonding between the polymeric matrix and the reinforcement. Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy, and scanning electron microscopy characterization and imaging techniques were used to prove that the ZnO nanoparticles were successfully modified prior to manufacturing the epoxy composites. While tensile testing showed that using pristine ZnO increases the composite's strength by 32.14%, the fracture toughness of the resin was improved by 9.40% when reinforced with ZnO functionalized with APTES. TGA showed that the addition of functionalized nanoparticles increases the material's degradation temperature by at most 7.31 ± 4.9°C using ZnO/APTES. Differential scanning calorimetry and dynamic mechanical analysis testing proved that the addition of any type of nanoparticles increases the resin's glass transition temperature by as much as 7.83°C (ZnO/APTES).     

Soluble network polymers based on trifluoropropyl-substituted open-cage silsesquioxane: Synthesis,properties, and application for surface modifiers

Fluorinated completely condensed polyhedral oligomeric silsesquioxanes (F-CC-POSSs) are widely utilized as surface modifiers for polymeric materials because of their polyhedral and fluorine-rich structures, which generate polymers with lower surface energies under molecular-level control. In contrast, their derivatives, fluorinated incompletely condensed or open-cage POSSs (F-IC-POSSs), have similarly intriguing structures, but their utilization for polymer synthesis remains undeveloped. Herein, fluorinated network polymers were prepared based on a 3,3,3-trifluoropropyl-substituted IC-POSSs via hydrosilylation polymerization with isobutyl- and phenyl-substituted IC-POSS under optimized conditions. In addition to their good thermal stability and tunable refractive indices, these polymers exhibited solution processability and their casting films showed excellent optical transparency, indicating their potential for constructing fluorinated polymers. Their utilization as surface modifiers was examined by addition to poly(methylmethacrylate) (PMMA) films. Intriguingly, modified PMMA films with 2.0 and 0.5 wt% addition showed similar hydrophobicity and surface energies to the films prepared with only fluorinated network polymers.     

Influence of magnetic casting on the permeability and anti-fouling properties of a novel iron oxide/alumina/polysulfone mixed matrix membrane

Novel mixed matrix membranes (MMMs) were fabricated using Fe₃O₄, and Al₂O₃ nanoparticles (NPs) were added to the polysulfone (PSf) and N-methylpyrrolidone (NMP) solution. The nanocomposite membranes were fabricated using the NIPS (non-solvent induced phase separation) method. In order to create preferential permeation pathways for water across the MMMs, membrane formation is accomplished with an external magnetic field. Using magnetic casting cause the targeted placement of NPs in the best location and orientation. The performance of the prepared membranes was examined in terms of pure water flux and fouling parameters. Magnetic casting considerably increased pure water flux and decreased the total resistance of the optimum mixed matrix membrane, which contains 0.2% wt. of Fe₃O₄ NPs to 1175 L/m²h and 13.4 * 10¹¹ (m⁻¹), respectively. This is explained by the ordering of magnetic nanoparticles on the membrane sub-layer cast under the magnetic field of 500 mT, which changed the sub-layer structure. Less rough membrane surface of the mixed matrix membranes offered preferable anti-fouling properties against fouling by BSA proteins. The characterization of fabricated membranes was carried out using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), energy dispersive X-ray (EDX), and water contact angle measurement methods.     

Simultaneous enhancements of mechanical properties and hydrophilic properties of polypropylene via nano‐silicon dioxide modified by polydopamine

This study is focused on the development of high‐performance composite materials based on nano silicon dioxide (nano‐SiO₂) modified by polydopamine (PDA). A facile one‐step method was developed to synthesize core–shell structured SiO₂@polydopamine (PDA) nanospheres. During the synthesis, a PDA shell was simultaneously coated on the SiO₂ nanospheres to form the core–shell nanostructure which was blended with polypropylene (PP) and β nucleating agent (β‐NA) to enhance both mechanical and hydrophilic properties. Nano‐SiO₂ particles modified by PDA (SiO₂@polydopamine) influence the crystallization of PP seriously. The results indicated that when 1%wt SiO₂@polydopamine was added, the impact strength of composite reached the maximum value 12.60k J/m² increasing 137% compared with PP, the bending strength and bending modulus decreased slightly reaching 41.85 MPa, and 2192 MPa, respectively, the composite possessed hydrophilic performance with the water contact angle of 88.32°. β nucleating agent was used in all formulations, the synergistic effect toward mechanical properties with SiO₂@polydopamine was studied. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45004.     

Poly(vinylidene-co-hexafluoropropylene) membrane modified with glass fibers and polyvinyl pyrrolidone: Mechanical and electrochemical properties

The polymer electrolytes based on poly(vinylidene-co-hexafluoropropylene) (PVDF-co-HFP) have been widely studied and applied in devices for its excellent electrochemical and mechanical properties. Here, porous PVDF-co-HFP membrane modified with glass fibers (GFs) and polyvinyl pyrrolidone (PVP) were fabricated by phase-transfer method. When the dosage of GFs exceeded 1 wt%, the composite membranes exhibited 6.11 MPa tensile strength. When the dosage of GFs and PVP reached 1% (PVP₁GF₁), respectively, the composite membranes in porous network structure possessed the highest electrolyte uptake of 251.02%, the thermal stability of 343°C and the ionic conductivity of 3.05 × 10⁻³ S cm⁻¹. Electrochromic device (ECD) was assembled with PVP₁GF₁ electrolyte, showing quick responses between the bleached and the color states within 3 s. The PVDF-co-HFP composite electrolyte was expected to be effective substitutes for liquid electrolytes used in ECDs.     

Effect of polyurethane sizing on carbon fibers surface and interfacial adhesion of fiber/polyamide 6 composites

Commercial epoxy sized carbon fibers (CFs) or unsized CFs have poor interfacial adhesion with polyamide 6 (PA6). Here, CFs are coated with polyurethane (PU) and their surface properties in terms of surface chemistry, contact angle, roughness, and morphology, are investigated. The results of Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy demonstrate PU sizing evidently increases the quantity of polar functional groups on the CFs surface. The surface energy of the PU sized fiber is calculated according to the Owens–Wendt method. Compared with unsized fibers, the contact angle of PU sized fibers is decreased while their total surface energy is increased, indicating superior wettability. Moreover, transverse fiber bundle tests are performed to determine the interfacial adhesion between the CFs and PA6 matrix. The transverse fiber bundle strength of unsized CF is measured to be 12.57 MPa. For PU sized CFs processed with sizing concentration of 1.2%, this value is increased to 24.35 MPa, showing an increase of more than 90%. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46111.     

Effect of phosphate ion on the textural and catalytic activity of titania–silica mixed oxide

Phosphate-modified TiO₂-SiO₂ mixed oxide catalysts have been prepared by varying the method of preparation, source and concentration of phosphate ion. The prepared catalysts were compared for their catalytic activity/selectivity in nitration of toluene. The characterisation of the catalysts was performed using X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermal analysis (TG–DTA), nitrogen adsorption–desorption methods, surface acid strength measured by Hammett indicator method, surface acid sites measured by amine titration method, and phosphate content measured by UV–VIS spectrophotometry. The XRD patterns revealed that phosphate ion stabilises the anatase phase up to 1173 K activation. FT-IR results show that phosphate species strongly bound bidentately, and that both the internal weakly H-bonded hydroxyl groups and free hydroxyl groups are present on TiO₂–SiO₂ mixed oxide support. Surface area and surface acidity are found to increase with the increase in phosphate loading up to 7.5 wt.% and thereafter the values decrease drastically. However, average pore radius and total pore volume shows the reverse order. Phosphated samples prepared using H₃PO₄ as the source of phosphate ion exhibit higher acidity, and surface area but lower porosity than the samples prepared from (NH₄)₃PO₄, though both the samples contain the same amount of phosphate (7.5 wt.%). Similar results were also observed when varying the method of preparation. TiO₂–SiO₂ samples prepared at pH=3 exhibit higher acidity and surface area but lower porosity than the samples prepared at pH=7. The acid strength of 7.5P/TiO₂–SiO₂ (H) is found to be stronger than that of 100% concentrated H₂SO₄. The material modified with phosphate ion was found to be an efficient and selective catalyst for solvent-free mono-nitration of toluene. Selectivity to the para-product is correlated with the porosity of the material.