TiO2 Loading Research Articles

Tensile and Morphology Properties of PLA/MMT-TiO<sub>2</sub> Bionanocomposites

The aim of this study is to produce PLA nanocomposites by solvent casting incorporating Montmorillonite nanoclays (MMT) and titanium dioxide (TiO2) nanoparticles. The effects of difference loadings of MMT in PLA and different loadings of TiO2 on mechanical and morphology properties were studied. The nanocomposites were prepared by solvent casting at different loadings of MMT (0, 2, 4, 6 and 8 wt %) and different loadings of TiO2 (1 and 3 wt %) respectively. The properties such as tensile properties (tensile strength, elongation at break, and modulus of elasticity) and morphology were determined. The results indicate that 4 wt% of MMT loading produced the best tensile properties. However, the incorporation of TiO2 showed an improvement in the modulus of elasticity of PLA/MMT nanocomposites mainly at 1 wt % loading of TiO2.

PLA/MMT-TiO<sub>2</sub> Bionanocomposites: Chemical Structure and Surface Wettability

Polylactic Acid (PLA) has been used widely in packaging application because of its biodegradability. The aim of this study is to produce PLA nanocomposites by solvent casting incorporating montmorillonite nanoclays (MMT) and titanium dioxide (TiO2) nanoparticles. The effect of different loadings of MMT in PLA and different loadings of TiO2 on chemical structure and surface wettability were studied. The nanocomposites were prepared by solvent casting at different loadings of MMT (0, 2, 4, 6 wt %) and different loadings of TiO2 (1 and 3 wt %) respectively. The chemical structure and surface wettability were determined. The absorption peaks in the range of 3550-3200 cm-1 had increased after incorporating of TiO2 and it indicated that there is the presence of stretching vibration of O-H groups. Moreover, increasing the percentage of TiO2 mass in the nanocomposites decreased the contact angle with water which led to increasing the wettability of the nanocomposites.

Restoration of pretreated palm oil mill effluent using TiO2 based photocatalytic system: An optimization study

Phenolic compounds found in pretreated palm oil mill effluent (pre-POME) pose severe threat to aquatic ecosystem and human health due to their build-up in the environment and high toxicity. Thus, the removal of phenolic compounds from pre-POME is necessary to preserve environmental quality and protect human health. In this paper, the optimized degradation of phenolic compound, gallic acid (GA) from pre-POME under visible light assisted TiO2 based photocatalysis is reported. TiO2 nanoparticles (NPs) were synthesized by chemical precipitation technique followed by characterization with X-ray diffraction (XRD), diffuse reflectance UV-Vis spectroscopy (DR-UV-Vis) and field emission scanning electron microscopy (FESEM). The effect of process variables such as loading of TiO2 and H2O2 dose on the degradation of GA from pre-POME was investigated and optimized using response surface methodology (RSM) based on central composite design (CCD). Spherical shaped anatase phase TiO2 NPs with size 45.47 nm and band gap (Eg) of 3.16 eV were obtained. The results demonstrated that both variables, TiO2 loading and H2O2 dosage showed positive effect on GA degradation. The highest removal of GA from pre-POME (71.20%), from 44.85 ppm of initial concentration was observed for the optimal TiO2 loading of 0.88 g/L, H2O2 dosage of 8.5 wt% and 2 h reaction under visible light irradiation. The use of H2O2 combined with TiO2 NPs indicated a great potential for the removal of GA, which has been pointed out as the major phenolic compounds in pre-POME.

Development of mixed matrix membrane comprising titanium (IV) oxide dispersed with octaisobutyl polyhedral oligomeric silsesquioxane

In designing mixed matrix membranes (MMMs) to improve gas separation performance, inorganic fillers such as titanium (IV) oxide (TiO2) nanoparticles are commonly added due to their excellent intrinsic properties and high affinity towards CO2. However, the addition of TiO2 nanoparticles causes the formation of agglomerates which deteriorate the gas separation properties of the membrane due to their high surface energy and Van der Waals forces. In this study, MMMs comprising octaisobutyl polyhedral oligomeric silsesquioxane (OPOSS) incorporated with TiO2 nanoparticles were successfully developed using phase inversion technique. MMMs were synthesized at different loadings of TiO2 and OPOSS. The effectiveness of OPOSS as a dispersant was determined by using SEM, EDS and single gas permeation analysis. The optimum amount of TiO2-OPOSS in the THF/DMAc casting solution was at 4wt% TiO2 and 2wt% of OPOSS, as the agglomeration of nanoparticles did not occur based on the morphology and gas separation performance. The membrane with the highest performance was achieved by 4/2-T/OPOSS, which is at 1.8 of CO2/CH4 gas selectivity. Based on the findings, it can be concluded that the OPOSS did play an important role in enhancing the dispersion of TiO2 nanoparticles in the polymer matrix as the TiO2 agglomerates were not seen upon addition of OPOSS.

Synthesizing C–N–P-tridoped TiO2 in a Salix psammophila-activated carbon body to enhance its regeneration performance

Loading TiO2 into an AC body via Salix psammophila pores. C, N, and P atoms were spontaneously doped into TiO2 lattices. MB removal ratio decreased by 11% after three trials. The synergistic effect of adsorption and photodegradation was enhanced.

Highly recyclable and super-tough hydrogel mediated by dual-functional TiO2 nanoparticles toward efficient photodegradation of organic water pollutants

A novel photocatalytic hydrogel was prepared by loading TiO2 nanoparticles (TiO2 NPs) onto the surface of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized chitin nanofibers (TOCNs), which were further incorporated into the polyacrylamide (PAM) matrix. The resultant hydrogel exhibited a macro-porous structure with a low density (~1.45 g/cm3) and high water content (~80%). The well-dispersed TiO2 NPs not only acted as a crosslinking agent for bridging the three-dimensional porous network structure, but also endowed the hydrogel with good catalytic activity. After the introduction of TiO2 accounting for 10 wt% of the hydrogel mass, the hydrogels showed compressive strength of 1.46 MPa at 70% strain, tensile stress of 316 kPa, tensile strain of 310%, toughness of 47.25 kJ/m3 and fatigue resistance. Compared with neat TOCN-PAM hydrogel, the uniaxial compressive and tensile strengths of the TiO2-TOCN-PAM10 hydrogel increased 6.35-fold and 3.70-fold, respectively. Furthermore, the removal of methyl orange (MO) was attributed to the synergistic effect of the adsorption and photocatalytic degradation of the hydrogels. The hydrogels adsorbed up to 8.5% of MO after 150 min of adsorption and a photocatalytic degradation rate of 97.3% achieved after 90 min of UV irradiation at pH = 2. Especially, the TiO2-TOCN-PAM10 hydrogel exhibited excellent recycling performance: its MO removal efficiency was around 96% even after 10 reuse cycles. The as-prepared hydrogels, with characteristics of excellent stretchability, photocatalytic activity and recyclability, are expected to be used in alleviating organic pollutants in practical wastewater treatments.

Nanowires embedded porous TiO2@C nanocomposite anodes for enhanced stable lithium and sodium ion battery performance

A porous carbon nanocomposite with embedded TiO2 nanowires (NWs) was synthesized using a two-step synthetic method in which carbon matrix was obtained by carbonizing a vacuum dried gel. This unique structure in which TiO2 nanowires uniformly distributed in and tightly bonded to the carbon matrix shortened the electron transport path and reduced the transmission resistance. Nanoporous structure ensured continuous transfer of Li+/Na+ and supplied a large specific surface area of 280.82 m2 g−1 to provide more active sites. Different from other existing works on TiO2@C anode materials with TiO2 loading higher than 60 wt%, the obtained very small amount of TiO2 (~12 wt%) improved the electrochemical and long-cycle performance of carbon substrate with TiO2 NWs embedded significantly, due to uniformly distributed TiO2 NWs throughout the carbon matrix. These TiO2@C composite anodes could deliver a specific capacity of 286 mA h g−1 at 0.3 C, 197 mA h g−1 at 0.15 C for lithium and sodium ion batteries, respectively. It maintained remarkably stable reversible capacities of 128 and 125 mA h g−1 for lithium and sodium ion batteries at 3 C during 2500 cycles, respectively. Smaller fluctuations and smoother curves demonstrated that sodium ion storage was more stable than lithium ion storage for the TiO2@C composite anode. In addition, the capacitive contributions of TiO2@C in both systems are quantified by kinetics analysis.

Ultrasound assisted oxidative deep-desulfurization of dimethyl disulphide from turpentine.

A promising approach of ultrasound assisted oxidative desulfurization (UAOD) was studied for deep desulfurization of simulated sulphated turpentine containing dimethyl disulphide (DMDS) as model pollutant. The effect of ultrasound parameters such as power (80-120W) and duty cycle (50-80%) as well as operating conditions as initial concentration (50-100ppm), volume (100-300ml) and temperature (28°C as ambient condition, 50-70°C) on the extent of desulfurization have been studied. The effect of addition of various oxidizing agents such as hydrogen peroxide over the range of 3-18g/L, Fenton reagent by varying FeSO4 loading from 0.75g/L to 1.75g/L at constant H2O2 loading and titanium dioxide (loading over the range 1-4g/L) in the presence of ultrasonic horn have also been investigated at laboratory scale. The addition of oxidizing agents in presence of ultrasound enhanced the extent of DMDS removal. The extent of desulfurization was found to be remarkably low for individual approaches as compared to combination approaches of US/oxidizing agents. The kinetic analysis revealed that oxidation follows first order kinetics. A significant increase in cavitational yield was observed for combination approach of US/H2O2/TiO2 (5.78×10-9g/L) compared to individual ultrasound approach (2.04×10-9g/L). Under best conditions of 120W power, 70% duty cycle, 50ppm initial concentration, 15g/L H2O2 loading and 4g/L TiO2 loading, 100% desulfurization was obtained at 23.19 Rs/L as the treatment cost. Based on the obtained results it can be concluded that US/H2O2/TiO2 approach is highly efficient desulfurization technique for deep desulfurization of simulated sulphated turpentine.

Preparation of TiO2 supported on MDF biochar for simultaneous removal of methylene blue by adsorption and photocatalysis

AbstractBACKGROUNDThis article reports for the first time the preparation and characterization of biochar/titanium dioxide (TiO2) composites by pyrolysis from medium‐density fiberboard (MDF) biomass. Their adsorptive and photocatalytic activities were evaluated by removal of methylene blue (MB) dye from aqueous solutions with and without UV‐light irradiation.RESULTSCharacterization results suggested that the composite have different intrinsic characteristics in relation to the precursors. The biochar and TiO2 amounts of the composite significantly affected its performance. The MB removal efficiency with 1 g L−1 of the composite with 10% w/w TiO2 (B10T sample) was 2.3 and 2.2 times faster than that the B5T and B1T samples, respectively, and 1.5 times faster than TiO2 alone.CONCLUSIONThe loading of TiO2 significantly enhanced the adsorption performance of the composite and factors such as specific surface area, pore volume and pore size of the biochar synergistically promoted the photocatalytic activity of TiO2, coupled with a lower band gap for all composites produced. Both adsorption and photocatalytic efficiencies were confirmed to contribute to the degradation of the aqueous solution of MB by the hydroxyl radical (•OH) in lower molecular mass by‐products. The synthesized composite is a promising alternative sustainable material for removing chemical contaminants, since the biochar used as a support comes from the waste of the furniture industry. © 2019 Society of Chemical Industry

Solar photocatalytic treatment of industrial wastewater utilizing recycled polymeric disposals as TiO2 supports

Heavily contaminated industrial wastewater is treated using a homemade compound parabolic reactor utilizing recycled polymeric disposals as TiO2 supports. The recycled polymeric materials include cotton, cotton lycra, polyamide, paper, polyethylene terephthalate, polypropylene, and polyurethane. The loading of TiO2 onto different support materials was investigated to identify the optimal composite. The TiO2/polyethylene terephthalate collected from Factory i (PETi) composite was selected because of its durability, strong polymer-TiO2 binding, and significant photocatalytic activity. Infrared and scanning electron microscopy characterizations confirm the strong binding and homogenous distribution of TiO2 particles over the PETi surface before and after the photocatalytic process. The solar photocatalytic treatment of the sample wastewater resulted in significant photobleaching. A significant reduction in the chemical oxygen demand (COD) and mineralization percentages of up to 42% were reported. The increased biological oxygen demand to COD ratios indicate the formation of new biodegradable species, enabling further normal biological treatment.

A comparative photocatalytic study of TiO2 loaded on three natural clays with different morphologies

In this work, a sol-gel method was used to load TiO2 nanoparticles on three clays (kaolinite, halloysite and palygorskite) with different morphologies (plates, tubes, and rods with micro tunnels), and then the photocatalytic performance of obtained clay-TiO2 composites for degradation of methyl orange was comparatively investigated. The results surprisingly show that the trend of photocatalytic performance of composites is opposite to that of special surface area of corresponding clays. By concentrated analysis of the loading status of TiO2, the lowest photocatalytic efficiency of palygorskite-TiO2 composite is mainly ascribed to (1) the aggregation of TiO2 nanoparticles on Pal surface, not the amount of TiO2 and (2) the relatively weak adsorption of Pal to methyl orange. The additional adsorption of hydroxyl surface of Kaol to methyl orange and little TiO2 in the lumen of Hal tube leads to the better photocatalytic performance of kaolinite-TiO2 composite than halloysite-TiO2 composite. Finally, kaolinite is proved to be an excellent carrier to support nano TiO2 resulting in a good photocatalytic performance and cycle stability, and the study can provide a direct guidance to select appropriate clay-photocatalyst composites for different practical applications.

Porous ceramic foam loading titanium dioxide for photocatalytic degradation of the methyl orange solution

Purpose The purpose of this paper is to provide an investigation on a new kind of photocatalytic material, namely, the porous ceramic foam loading titanium dioxide, which can make an effective photocatalytic degradation of the methyl orange (MO) solution in the wastewater. Design/methodology/approach The natural zeolite powder has been used as the primary raw material to produce a sort of lightweight porous ceramic foam by impregnating polymer foam in slurry and then sintering. With the sol-gel method, a kind of open-cell reticular porous ceramic foam loading TiO2 film was obtained having a good photocatalytic action, and the resultant porous composite product presents the bulk density of 0.3~0.6 g/cm3 to be able to float on water. Findings The MO could tend to be completely degraded in the solution with a certain concentration by the TiO2-loaded ceramic foam irradiated with ultraviolet light, and this composite foam was found to have high degradation efficiency for the MO solution in a wide range of pH. Originality/value This work presents a TiO2-loaded ceramic foam that can effectively photo-catalyze to degrade the MO in water, and the degradation efficiency were examined under different conditions of the MO solution with various pH values.

Preparation and Characterisation of PVA+TiO2 Nanofiber by Electrospinning Technique

In the present work PVA+TiO2 nanofibers were prepared by electrospinning technique. Structural and Functional groups were carried out by X-Ray diffraction and FTIR technique. The optical analysis was analysed by UV-DRS and Photoluminscence studies. Morphology and compositional were characterized by FESEM and EDS analysis. From Structural analysis shows PVA+TiO2 anatase crystal structure and crystallite size are nanometers. The FTIR technique was used to find out the functional groups present in the prepared set of samples. The optical analysis shows above 70% transparency in the visible region. From the PL analysis titanium and oxygen vacancies are found to be 375 and 526 nm. FESEM analysis of the annealed samples shows the uniformity of nanofibers without any beads which is attributed to the interaction of TiO2 particles with the PVA matrix. From the compositional analysis, the atomic weight percentage of Ti and O increases with the TiO2 loading in PVA.

Functionalization of renewable bamboo charcoal to improve indoor environment quality in a sustainable way

Abstract The increasing demand for health calls for a bacteria-free environment with proper humidity content. A composite with both bactericidal and humidity control properties is promising in an environmental and economic way for this purpose. In this paper, renewable bamboo charcoal (BC) was used to prepare this multifunctional material by loading silver doped titanium dioxide (Ag/TiO2) with a sol-gel method. The synthesized composite (Ag/TiO2-BC) was characterized by X-ray diffraction (XRD) and scanning electron microscope with energy disperse spectroscope (SEM-EDS) analyses. Antibacterial performance was evaluated by bactericidal rate on both Escherichia coli and Staphylococcus aureus strains. Photocatalytic activity was studied by methylene blue (MB) removal performance. Humidity adsorption and response speed were determined to evaluate the humidity control performance. Results show that Ag promote the transformation of rutile to anatase. SEM-EDS analysis proves the successful loading of Ag/TiO2 on BC surface. Both Ag doping on TiO2 and Ag/TiO2 loading on BC show significantly promoting effects on the bactericidal rate of Ag/TiO2-BC for both strains. MB removal results indicate that TiO2 loading on BC surface increases removal ratio while Ag doping on TiO2 shows further improvement. Humidity tests show that Ag, Ag/TiO2 and calcination temperature slightly decrease the humidity adsorption of Ag/TiO2-BC due to the decreased specific surface area and pore volume determined from nitrogen adsorption tests. However, all samples present prompt humidity adsorption and desorption responses. The overall results show that this biomass deprived composite could be used as a self-control material with bactericidal and humidity control functions.

Fabrication of TiO2 embedded ZnIn2S4 nanosheets for efficient Cr(VI) reduction

Various TiO2/ZnIn2S4 composites with an embedded structure have been developed by a facile one-pot synthesis. The activities of all samples were estimated by photocatalytic reduction of Cr(VI) under visible light (λ>420 nm). Results showed that the electrostatic interaction and self-assembly effect make TiO2 nanoparticles inserting into ZnIn2S4 nanosheets. The resulting TiO2/ZnIn2S4 composites show much better photocatalytic performance for Cr(VI) reduction than that of pristine TiO2 and ZnIn2S4. Especially, the photocatalytic efficiency of T/ZIS-0.3 (TiO2 loading of 30 wt%) is approximate 3 times as high as that of pristine ZnIn2S4 (TiO2 exhibited almost no activity). The embedded structure of TiO2/ZnIn2S4 offers apparent increase of specific surface area, visible-light absorption and electrons transfer efficiency, which are responsible for the boosted photocatalytic activity. This work would inspire researchers to construct high-efficiency semiconductor composites for photocatalytic environmental governance.

Photocatalytic degradation of gaseous toluene using self-assembled air filter based on chitosan/activated carbon/TiO2

Photocatalytic filters are integrated with air purifiers and ventilation systems to remove volatile organic compounds (VOCs) from indoor air. However, the filters, generally prepared by dip or spray coating, are less stable as the deposited TiO2 NPs are prone to be blown off by treated air. In the present study, we propose a novel filter preparation method based on self-assembly of activated carbon (AC) and TiO2 on non-woven polyethylene terephthalate (PET) fabric using chitosan (CS). The prepared filter (CSAT-PET) was characterized for morphological and chemical properties which revealed the homogeneity and chemical bonding of deposited TiO2. Photocatalytic activity of the prepared filter was evaluated for toluene degradation (200–600 ppb) under dark and UV illumination. Toluene removal efficiency reached 91% over CSAT-PET, while it was only 62% over pure TiO2 filter. About 40% of toluene removal was achieved by adsorption on CSAT-PET. Furthermore, CSAT-PET showed robust performance for selected face velocity ranging from 0.5 to 1.5 m/s and, the reaction rate followed Langmuir-Hinshelwood model. FTIR study identified benzaldehyde and benzoic acid as adsorbed intermediates. A UV-induced filter regeneration partially released the adsorbed species. CSAT-PET showed consistent toluene removal and intact morphology over five degradation cycles. The Box-Behnken design (BBD) in RSM was applied to optimize the filter preparation method. The optimum values of TiO2, AC and CS loading were 38.3 g/m2, 52.6 g/m2 and 2.06% (w/v), respectively which exhibited highest removal efficiency for toluene (93%). The proposed methodology can be adapted to fabricate low-cost, stable, and reusable photocatalytic filter for air purification applications.

Study on V2O5-WO3-TiO2 catalytic filter for de-NO and particle separation

V2O5-WO3-TiO2 catalytic filter was prepared for particle separation and denitration. TiO2 was supported on mullite fiber filtration ceramic (FFC) by homogeneous precipitation method and V2O5-WO3 denitration catalyst was loaded on TiO2/FFC by impregnation method using the solution of V and W precursors. The BET surface area of TiO2/FFC measured by N2 adsorption was increased with TiO2 loading. The results indicated that the surface modification by anatase TiO2 improved the BET surface area of filters. The optimal mass ratio of V2O5 to WO3 with 1:1 and catalyst loading of 7.5 wt% were determined. The performance tests for V2O5-WO3-TiO2 catalytic filters showed that NO conversion was more than 80% and filter resistance at the filtration velocity of 1 m min−1 was 415 Pa. Moreover, the effects of filtration velocity and SO2 or H2O poisoning on NO conversion were investigated. Catalytic filters still showed approximately 80% NO conversion even if the filtration velocity reached 1.5 m min−1. NO conversion decreased to 68% in the presence of 300 ppm SO2 and 10 vol% H2O at 280 °C, but it could be recovered to 85% after the removal of SO2 and H2O.

Use of Au/N-TiO2/SiO2 photocatalysts in building materials with NO depolluting activity

Abstract Two factors are key in the design of a TiO2 photocatalyst for building materials that meets the requirements for environmental applications: the TiO2 light absorption restricted to UV and its poor adhesion to the substrates. In this work, two strategies of TiO2 modification, nitrogen doping and AuNPs deposition, were combined in order to promote the TiO2 photoactivity under solar radiation. By the other hand, the Au/N–TiO2 photocatalysts were incorporated in a silica sol allowing their application by spray on three different building material substrates (limestone, granite and concrete), where the sol spontaneously produced Au/N–TiO2/SiO2 well-adhered coatings. The samples photoactivity was evaluated by dye degradation tests and NO abatement measurements. The obtained results demonstrated that the AuNPs considerably enhanced the photoactivity of N–TiO2, doubling the amount of NOx removed under UV–visible light. In addition, the role of the substrate and the TiO2/SiO2 ratio of the coating were also investigated. The coatings practically triplicated their depolluting effectiveness on concrete in comparison with their application on limestone. A direct correlation between the TiO2 loading and the photoactivity was observed, increasing NOx abatement by a factor of 1.3 when the Au/N–TiO2 loading of the coating was raised from 10 to 25%. However, the Au presence can induce evident colour modifications of the treated substrates that can limit the product application on certain substrates.

Size-tunable TiO2 nanoparticles in mesoporous silica: Size-dependent performance in selective photo-oxidation

In order to understand the effect of nanoparticle size on photocatalytic activity in gas phase propane oxidation, TiO2 nanoparticles embedded in TUD-1 mesopores were prepared with a high degree of size control in the range 3–8 nm. One sample of TiO2-TUD-1 was prepared with Ti/Si ratio of 2.5, and during the synthesis, it was divided into four parts and hydrothermally treated for different times 8–24 h. The produced samples were characterized by means of XRD, HR-TEM, N2 sorption, and DR-UV-Vis spectroscopy. Characterization data showed that the size of the TiO2 nanocrystals is increasing with the hydrothermal treatment time. The photocatalytic activity of the four investigated samples, with identical TiO2 loading, was performed under the illumination of ultraviolet radiation λ = 335 nm, selectively activating the nanoparticles. Results showed that the initial reaction rate in photocatalytic oxidation of propane was found to be smaller for the TiO2 nanoparticles with an average size of 3.5 nm as compared to the TiO2 nanoparticles with an average size of 7.5 nm. However, the larger total available surface area lead to a higher propane consumption with higher photochemical selectivity toward acetone (desired product), as compared to the 7.5 nm particles.

Anodic Titanium Dioxide Nanotubes for Magnetically Guided Therapeutic Delivery

Hollow titanium dioxide (TiO2) nanotubes offer substantially higher drug loading capacity and slower drug release kinetics compared to solid drug nanocarriers of comparable size. In this report, we load TiO2 nanotubes with iron oxide nanoparticles to facilitate site-specific magnetic guidance and drug delivery. We generate magnetic TiO2 nanotubes (TiO2NTs) by incorporating a ferrofluid containing Ø ≈ 10 nm iron oxide nanoparticles in planar sheets of weakly connected TiO2 nanotubes. After thermal annealing, the magnetic tubular arrays are loaded with therapeutic drugs and then sonicated to separate the nanotubes. We demonstrate that magnetic TiO2NTs are non-toxic for HeLa cells at therapeutic concentrations (≤200 µg/mL). Adhesion and endocytosis of magnetic nanotubes to a layer of HeLa cells are increased in the presence of a magnetic gradient field. As a proof-of-concept, we load the nanotubes with the topoisomerase inhibitor camptothecin and achieve a 90% killing efficiency. We also load the nanotubes with oligonucleotides for cell transfection and achieve 100% cellular uptake efficiency. Our results demonstrate the potential of magnetic TiO2NTs for a wide range of biomedical applications, including site-specific delivery of therapeutic drugs.