High Length-diameter Ratio Research Articles

Design and motion control of a tendon-driven continuum robot for aerospace applications

Continuum robots are flexible and compliant. Compared to the case in conventional articulated manipulators, the driving unit can be placed outside the workspace of the robot, so that the motion orientation has a relatively complete linear configuration flow, which can be applied to a special environment with narrow and multiple obstacles such as aerospace. This study presents the development process of a tendon-driven continuum robot (TCR) with a high length-diameter ratio. The skeleton structure which imitates a snake is composed of continuous joints in series. The driving device is operated by using a tendon-driven method, which reduces the complexity of the driving box and control system significantly. The diameter of the robot is designed to be 5 mm, which enables it to work in a narrow and slender space with certain flexibility. Subsequently, a kinematic model of the robot is established. The mode function backbone method is applied to realize TCR trajectory planning. An idea of segmented solving is adopted to achieve trajectory tracking control of the continuum robot. Finally, a prototype of the continuum robot is produced, and the rationality of the robot design and the effectiveness of the motion control method are verified through trajectory simulations and experiments. The robot can perform inspection tasks within a narrow gap of 20 mm with good environmental adaptability.

Improved uniformity of atomic-layer-deposited HfO2 film along the length of glass monocapillary with high length-diameter ratio

It has been a difficult to deposit a uniform film on the inner surface of monocapillary due to the high length-diameter ratio. Atomic layer deposition (ALD) shows great potential to coat conformal film on complex substrates. However, it is still a challenge to coat uniform film along the length of the capillary for regular deposition parameters. In this work, HfO2 film was deposited inside monocapillary via ALD. The film uniformity along the monocapillary was investigated by cross-section scanning electron microscope (SEM) images and the bond states of one of the HfO2 films were studied via X-ray photoelectron spectroscopy (XPS). Using the routine deposition parameters, the gas flowing through the monocapillary is controlled to be small, large and medium qualitatively by covering some of the inlets or outlets, changing the connection between monocapillary and outlets simply. SEM results demonstrate that smooth HfO2 film with uniform thickness can be acquired on the inner surface of monocapillary with length-diameter ratio 200 (length 10 cm and inner diameter 0.5 mm). XPS results show that Hf hydroxide is generated when the gas flowing through the monocapillary is large.

NiCo-compounds inside and outside N-doped carbon nanotubes to construct a double-enhanced hierarchical structure for high energy density supercapacitors.

Attaining a high energy density that aligns with practical application requirements is a crucial indicator in the advancement of supercapacitors. In this paper, a hybrid hierarchical electrode structure of N-doped carbon nanotube (NCNT) spheres encapsulated with NiCo-Se nanoparticles (NPs) and coated with nickel-cobalt layered double hydroxide (NiCo-LDH) multilayer nanosheets was successfully synthesized on a nickel foam (NF) substrate. The self-supporting strategy enables nickel-cobalt Prussian blue analogues (Ni-Co PBAs) to be directly attached to the NF surface, which results in fluffy NCNTs with a high length-diameter ratio and considerable yield and greatly enhances the conductivity of the electrode material. The synergistic interaction between the dual transition metal compounds inside and outside the NCNTs enables the hybrid electrode material to achieve an impressive specific capacity of 1899 F g-1 (211.0 mA h g-1) at 1 A g-1. The asymmetric supercapacitor (ASC) exhibits an excellent energy density of 57.6 W h kg-1 at a power density of 798 W kg-1. This study not only provides an attractive strategy for obtaining CNTs with excellent properties from Ni-Co PBA and synthesizing hybrid electrodes with efficient synergistic effects, but also achieves a high energy density that aligns with the practical application demands of supercapacitors.

An Ultrathin CNFs/CF Composite and the Performance of Electromagnetic Interference Shielding

The catalyst layer was introduced by a novel slurry impregnation process. In this process, phenolic resin, Ni particles and SiO2 particles are acted as adhesives, catalysts and dispersants, respectively. CNFs which have a high length-diameter ratio were in situ grown on the surface of carbon fabrics via the CVD method. The microstructure, electrical conductivity, skin depth and electromagnetic interference shielding effectiveness (EMI SE) of CNFs/CF under different reaction times were investigated. The optimal process of CNFs/CF was obtained at 800[Formula: see text]C for reacting 15[Formula: see text]min. In this condition, CNFs have a good graphitization degree and the diameter is around 25[Formula: see text]nm. Since the CNFs/CF composite possesses numerous channels, the electrical conductivity increases and the skin depth decreases. The electromagnetic (EM) waves could be trapped and attenuated, yielding outstanding EM shielding effectiveness. The total shielding effectiveness (SE[Formula: see text] values were significantly under the ultrathin thickness. Consequently, the specific SE[Formula: see text] values of CNFs/CF reached 172.9 dB/cm, which means that the EM shielding effectiveness is excellent.

Constructing green superhydrophilic and superoleophobic COFs-MOFs hybrid-based membrane for efficiently emulsion separation and synchronous removal of microplastics, dyes, and pesticides

Oil spills and micropollutants have become thorny environmental issues, posing serious threat to ecosystem and human health. To settle such dilemma, this study successfully constructed a robust and environmentally-friendly MOFs-COFs hybrid-based membrane (FS-50/COF(MATPA)-MOF(Zr)/PDA@PVDF) for the first time through solution synthesis and solvothermal method, combined with surface modification of FS-50 molecule. Importantly, we employed a simple two-step strategy to obtain the high-aspect-ratio MOFs fibers: (1) solvent regulation to generate smaller needle-like whiskers during the in-situ growth of MOFs on COFs; (2) high pressure induced directional crystallization in filtration process. The introduction of polydopamine (PDA) greatly improved the adhesion between coating and PVDF membrane. The in-situ growth of high length-diameter ratio MOFs fibers on blocky COFs greatly enhanced the specific surface area of MOFs-COFs hybrid, thus provided sufficient absorption sites. The functional groups of FS-50 endowed the hybrid membrane with superhydrophilicity and superoleophobicity, which facilitated to selectively penetrate water molecules and repel non-polar pollutants. The separation efficiency and decontamination mechanism of hybrid membrane to the simulated oily wastewater (containing various MPs, dyes, and pesticides) were investigated through experiments and theoretical calculations. The hybrid membrane could selectively and synchronously adsorb various dyes (20 mg/L–120 mg/L, almost 100% removal) and pesticides (10 mg/L for DIF and TET, adsorption rates 93.2% and 90.9%, respectively) from oil-water emulsion (50 mL). The large-scale coated sponge (6 cm × 4.5 cm × 3 cm) could quickly achieve separation of oil-water mixture (almost 100%) with a water permeability of more than 162 L m−2·h−1·bar−1, and simultaneously remove various MPs (PP-2000, PP-100, PE-2000, PS-100, 0.2 g/300 mL for each), Sudan Ⅲ (C0 = 200 mg/L), and DIF (C0 = 10 mg/L) from a simulant oily wastewater (300 mL), with the removal rates of almost 100% for MPs, 99.7% for Sudan Ⅲ, and 95.8% for DIF. Furthermore, we elucidated the removal mechanism of pesticide and dyes through simulating the theoretical adsorption energy and potential adsorption sites. The hybrid membrane not only provides a promising candidate for the removal of multiple pollutants from oil-water emulsion, but also opens a new strategy for achieving efficient and clean aquatic environment restoration.

In situ synthesis of silver nanoparticles with controllable size distribution and high content in bagasse nanocellulose hydrogel

Developing an environment-friendly preparation method for silver nanoparticles (AgNPs) composite is significant. However, it remains challenges in size adjustment and content improvement of AgNPs. Here, the NaIO4 oxidation and TEMPO-mediated oxidation were applied to bagasse pulp to prepare nanocellulose (NC) with both carboxyl and aldehyde groups. The aldehyde content of NC could be adjusted in the range of 0.21–1.45 mmol/g by different NaIO4 oxidation times. When the carboxyl groups were protonated, NC with a high length-diameter ratio could construct stable hydrogels in a low concentration at 0.5 wt%. The NC hydrogels showed excellent in situ synthesis ability of AgNPs with abundant pore structure. By regulating the carboxyl group content of NC, the size distribution of synthesized AgNPs could be controlled in the range of 7.14–28.6 nm with high content of 6.79–11.0 %. The NC/AgNPs composite hydrogel exhibited high catalytic degradation activity for 4-nitrophenol and antibacterial activity. This approach for constructing NC hydrogel paves the way for AgNPs composite products with adjustable sizes and high contents.

High-efficiency air filter aerogel resembling blood cell with heterogeneous epitaxial growth of zeolitic imidazolate framework-8 anchored on tunicate cellulose nanofibers for integrated air cleaning

Metal-organic frameworks (MOFs) possess highly ordered porous structures and photocatalytic capabilities, making them ideal for air cleaning and antibacterial applications. However, the crystallization kinetics of MOFs constrain their crystal structure, which limits their practical usage for air cleaning and other applications. Herein, we present a non-MOF template strategy to achieve heterogeneous epitaxial growth of zeolitic imidazolate framework-8 (ZIF-8) on cellulose extracted from tunicate. TEMPO-oxidation tunicate cellulose nanofibers (TOCNFs) have a high length-diameter ratio (>1000) and negatively charged carboxyl and hydroxyl groups that serve as suitable templates to promote heterogeneous nucleation of the ZIF-8 crystal, thereby resulting in the fabrication of a unique porous structure resembling blood cell. The ZIF-8@TOCNFs aerogel shows good porosity performance, achieving a maximum particulate matter (PM) removal efficiency of 95.80 % with a low pressure drop of 14 Pa at an air-flow velocity of 0.34 m/s. Compared to other works and commercial filters, ZIF-8@TOCNFs aerogel exhibits a higher quality factor (QF) of up to 0.197 Pa−1. Furthermore, ZIF-8@TOCNFs aerogel also demonstrates remarkable antibacterial and antiviral performance without UV photocatalysis. This unique design of ZIF-8@TOCNFs aerogel opens a new avenue for non-MOF template growth of MOF-on-MOF heterostructures and provides a novel strategy for preparing high-performance air filters with an integrated performance of low pressure drop, high removal efficiency and QF, great antibacterial and antiviral properties.

Construction of nickel/cobalt encapsulated by N-doped carbon nanotubes for high performance supercapacitors

Armour-like nanomaterials could maintain high activity and stability under harsh conditions. In this paper, armour-like electrode material, Ni/Co encapsulated by N-doped carbon nanotubes (NCNTs-Ni/Co), are prepared with NiCo prussian blue analogue (PBA) as precursor and template. In particular, the NCNTs-Ni/Co formed at a C3H6 flow rate of 0.2 L min−1 exhibited a high length-diameter ratio and excellent supercapacitor performance. The specific capacitance at 1 A g−1 reached 231.2 F g−1 and the retention rate at 20 A g−1 was 69 %. The asymmetric supercapacitor (ASC) assembled from NCNTs-Ni/Co/0.2 and activated carbon (AC) exhibited a power density of 38.3 Wh kg−1 at 800 W kg−1 and retained the highest specific capacitance of 87.3 % after 10,000 charge/discharge cycles. In general, this study gives a new idea for the derivation of structures with excellent electrochemical performance and unique structure from PBA.

One-Step Preparation of Si-Doped Ultra-Long β-Ga2O3 Nanowires by Low-Pressure Chemical Vapor Deposition

In this work, we prepared ultra-long Si-doped β-Ga2O3 nanowires on annealed Al2O3-film/Si substrate by low-pressure chemical vapor deposition (LPCVD) assisted by Au as catalyst. The length of nanowires exceeds 300 μm and diameters range from ~30 to ~100 nm in one-dimensional structures. The nanowires show good crystal quality and exhibit (201) orientation, confirmed by transmission electron microscopy and X-ray diffraction analysis. The PL spectrum obtained from these β-Ga2O3 nanowires has three obvious blue luminescence peaks at 398 nm (3.12 eV), 440 nm (2.82 eV), and 492 nm (2.51 eV). The electrical properties obtained from Si-doped β-Ga2O3 nanowires exhibit good conductivity. A metal-semiconductor-metal device is made by using Ti/Au as the electrode, and the device current reaches 200 pA at a bias voltage of 3 V. Our results show that ultra-long Si-doped β-Ga2O3 nanowires can be grown directly on the surface of Al2O3-film/Si substrates. These nanowires have a very high length-diameter ratio and good electrical properties. A possible mechanism for Si doping is also presented.

Bio-inspired mechanically robust superhydrophobic polypropylene surfaces embedded with silicon carbide whiskers for enhancing bactericidal performance

The risk of spread of antibiotic-resistant bacteria leads to the growth of implant-associated infection, necessitating the large-scale fabrication of antibacterial materials. The successfully synthetic superhydrophobic and bactericidal materials without durable surfaces are easy to destroy and so difficult to use in a large-scale production in terms of manufacturing costs in performing experiments and processes. In this work, two kinds of microfeatured sieves dipped with high length-diameter ratio silicon carbide whiskers (SiCw) are used as templates for the fabrication of micropillared polypropylene (PP) surfaces embedded with nanospiked SiCw exposed in different postures of standing via a simple low-cost micro-compression molding method. The standing SiCw nanospikes endow the micropillared PP surfaces with a high contact angle (CA) of 153.9° decreased by less than 8° after a wear distance of 1500 mm, exhibiting robust antiwetting and antifriction properties. Further, the nanospiked micropillared PP surfaces exhibit extremely low adhesion and moderate antibacterial efficacy. The micro-/nanoconstructed PP surfaces is expected to approach towards large-scale industrial production for biomedical applications.

3D radially-grown TiO2 nanotubes/Ti mesh photoanode for photocatalytic fuel cells towards simultaneous wastewater treatment and electricity generation

Photocatalytic fuel cell (PFC) represents a clean environment and energy technology to directly recover chemical energy contained in wastewater for electricity generation by using solar energy. It is advantageous for the PFC to adopt the TiO2 nanotube array photoanodes that usually grow on planar Ti substrates. But low specific surface area and light utilization limit the improvement in the PFC performance. This work is directed to the development of a 3D radially-grown TiO2 nanotubes/Ti mesh photoanode. The Ti mesh substrate provides a large specific surface area for growing TiO2 nanotubes and benefits light scattering, while TiO2 nanotubes with high length-diameter ratio enhances electron transfer. Because of these merits, the staggered PFC with the 3D radially-grown TiO2 nanotubes/Ti mesh photoanode yields a maximum power density (PMAX) of ∼0.074 mW/cm2, which is about 6.2 and 1.6 times as those with the TiO2 nanoparticles/Ti mesh and TiO2 nanotubes/Ti foil photoanodes, respectively. Increasing the mesh density of Ti mesh is synergic to improve the cell performance due to increased surface area and light utilization. The optimal PMAX of the ordinary PFC reaches as high as 0.15 mW/cm2 when using the Ti mesh of 300 per inch. Notably, using Ti mesh as a substrate makes it easy to integrate multiple Ti meshes to form a stacked 3D photoanode, which shows excellent performance when feeding various pollutants even with biogas slurry. Besides, good stability of the developed photoanode is also demonstrated. This work offers an innovative strategy for developing high-performance 3D structured photoanode for photoelectrochemical systems.

Silk nanofibril as nanobinder for preparing COF nanosheet-based proton exchange membrane

Two-dimensional covalent organic framework nanosheets (CONs) with ultrathin thickness and porous crystalline nature show substantial potential as novel membrane materials. However, bringing CONs materials into flexible membrane form is a monumental challenge due to the limitation of weak interactions among CONs. Herein, one-dimensional silk nanofibrils (SNFs) from silkworm cocoon are designed as the nanobinder to link sulfonated CON (SCON) into robust SCON-based membrane through vacuum-filtration method. Ultrathin and large lateral-sized SCONs are synthesized via bottom-up interface-confined synthesis approach. Benefiting from high length-diameter ratio of SNF and rich functional groups in both SNF and SCON, two-dimensional (2D) SCONs are effectively connected together by physical entanglement and strong H-bond interactions. The resultant SCON/SNF membrane displays dense structure, high mechanical integrity and good stability. Importantly, the rigid porous nanochannels of SCON, high-concentration –SO3H groups insides the pores and H-bonds at SCON–SNF interfaces impart SCON/SNF membrane high-rate proton transfer pathways. Consequently, a superior proton conductivity of 365 mS cm−1 is achieved at 80 °C and 100% RH by SCON/SNF membrane. This work offers a promising approach for connecting 2D CON materials into flexible membrane as high-performance solid electrolyte for hydrogen fuel cell and may be applied in membrane-related other fields.

NiCo-Se nanoparticles encapsulated N-doped CNTs derived from prussian blue analogues for high performance supercapacitors

Herein, N-doped carbon nanotubes (CNTs) encapsulating NiCo-Se nanoparticles (NPs) are assembled to spheres (NCNTs/NiCo-Se), which are successfully synthesized by using Ni-Co prussian blue analogues (PBAs) as templates and precursors. It is rare to derive CNTs from PBAs by means of C3H6 among the reported work and the structure evolution of NCNTs spheres derived from PBAs is exhibited. The high flow rate of N2 and C3H6 tend to cause short CNTs and large diameter of CNTs, respectively, owing to the dual-effect of diffusion and deposition of C atoms. Due to the advantage superposition of CNTs with high length-diameter ratio and NiCo-Se NPs, NCNTs/NiCo-Se gets excellent capabilities of charge transfer, diffusion efficiency, and electrochemical reactions. When the C3H6/N2 is 0.2/0.3 L min−1, the as-fabricated NCNTs/NiCo-Se deliver a substantially appreciable specific capacitance of 171.1 mAh g−1 (current density of 1 A g−1). The asymmetric supercapacitor (ASC) yields a maximum energy density of 55 Wh kg−1 at a power density of 801 W kg−1. In general, this work offers an attractive route to synthesize CNTs composites from PBAs.

Sealing Mechanism Based on Force Chain and Experimental Investigation of Sealing Fractures

Abstract Lost circulation often occurs in fractured formations, which was a main technological problem during drilling. Conventional lost circulation material (LCM) was often used to form a plugging zone to prevent fluid loss during drilling. The formed seal was a granular material system composed of LCMs. This paper presented the physical mechanism of the force chain within the plugging zone. The seal performance is related to the properties of LCMs. A device for testing seal performance of LCMs with long fracture was developed. The effects of LCM performance on seal integrity were investigated using a plugging device with long fracture. The results showed that the wide particle size distribution (PSD) of LCMs tended to form a strong force chain network structure within the sealing zone. Increasing the stiffness and roughness of LCMs resulted in higher breaking pressure. The addition of fiber with high length-diameter ratio could improve the shear strength of the sealing zone and form a strong force chain network structure, and it can reduce fluid loss.

Modification of graphene aerogel with titania nanotubes for efficient methylene blue adsorption kinetics

Titania nanotubes (TNTs) with high length–diameter ratio are incorporated into reduced graphene oxide (rGO) aerogel to modify the porous structure of the obtained rGO/TNTs aerogel for efficient methylene blue (MB) adsorption. A hydrothermal method along with freeze drying is applied for the preparation of the rGO/TNTs composite aerogel. The uniformly dispersed TNTs in rGO matrix can effectively support the network structure and hinder the π–π bonding interaction between graphene sheets, thus resulting in a three-dimensional mesoporous network with high specific surface area. The rGO/TNTs aerogel shows favorable adsorption property toward MB and the maximum adsorption capacity can be 380.7 mg g−1 with the adsorption efficiency of 92.2%. Besides, the adsorption kinetic analysis reveals that a dispersion process is found to be the rate-limiting step when the adsorbent dosage is low. With the increase of adsorbent content, chemical sorption such as the π–π interaction or the reaction of the polar functional groups between MB and rGO–TNTs-C aerogel becomes the rate-limiting step.

Excellent microwave absorption performances of high length-diameter ratio iron nanowires with low filling ratio

Reducing the filling content of high-density ferromagnetic particles is a key prerequisite for obtaining lightweight absorbers. To this end, large iron nanowires (Fe NWs) with high length-diameters, uniform length of approximately 21 μm and diameters of approximately 60 nm were synthesized through a facile magnetic field-induced in situ reduction method without templates and surfactants. The phase structures, and micromorphology of the high-aspect-ratio Fe NWs were analyzed, and the electromagnetic properties of Fe NWs-paraffin composites were measured with a vector network analyzer at 2–18 GHz. The Fe NWs-paraffin composite with a low filler loading also exhibited satisfactory microwave absorption performance, and the composites filled with 20 wt.% of as-prepared Fe NWs shows a minimum reflection loss (RLmin) of −44.67 dB at 2.72 GHz and effective absorption bandwidth (EAB) with reflection loss below −10 dB reached 8.56 GHz at a layer thickness of 1.42 mm. At a thickness of 3 mm, the RLmin value and EAB (RL ⩽ −10 dB) reached −29.74 dB and 3.28 GHz (3.84–7.12 GHz), respectively. This study suggests that Fe NWs with high-aspect-ratios have promising microwave absorbing applications, and provides a good reference for the preparation of ferromagnetic metal-based lightweight electromagnetic wave-absorbing materials.

Enhancing the Thermo-Mechanical Property of Polymer by Weaving and Mixing High Length–Diameter Ratio Filler

Improving thermo-mechanical characteristics of polymers can efficiently promote their applications in heat exchangers and thermal management. However, a feasible way to enhance the thermo-mechanical property of bulk polymers at low filler content still remains to be explored. Here, we propose mixing high length-diameter ratio filler such as carbon nanotube (CNT), boron nitride (BN) nanotube, and copper (Cu) nanowire, in the woven polymer matrix to meet the purpose. Through molecular dynamics (MD) simulation, the thermal properties of three woven polymers including woven polyethylene (PE), woven poly (p-phenylene) (PPP), and woven polyacetylene (PA) are investigated. Besides, using woven PE as a polymer matrix, three polymer nanocomposites, namely PE-CNT, PE-BN, and PE-Cu, are constructed by mixing CNT, BN nanotube, and Cu nanowire respectively, whose thermo-mechanical characteristics are compared via MD simulation. Morphology and phonons spectra analysis are conducted to reveal the underlying mechanisms. Furthermore, impacts of electron-phonon coupling and electrical field on the thermal conductivity of PE-Cu are uncovered via two temperature model MD simulation. Classical theoretical models are modified to predict the effects of filler and matrix on the thermal conductivity of polymer nanocomposites. This work can provide useful guidelines for designing thermally conductive bulk polymers and polymer nanocomposites.

Tension–Compression Asymmetry of Superelasticity in Unidirectionally Solidified Cu-Al-Mn Shape Memory Alloy

The unidirectionally solidified Cu-Al-Mn shape memory alloy with strong -oriented texture along the solidification direction and high length-diameter ratio columnar-grained structure exhibits excellent superelastic properties compared to the Ni-Ti alloys. In this paper, the tension–compression asymmetry of unidirectionally solidified Cu71Al18Mn11 alloy was researched by the geometrically nonlinear theory and superelastic experiments. The results show that the tension–compression asymmetry of the alloy has a significant anisotropy. The theoretical asymmetry ratio of transformation strain along reaches 14.2%, which is larger than other orientations. The tension and compression superelastic experiment research of unidirectionally solidified Cu71Al18Mn11 SMA along the direction parallel ( grain orientation) or perpendicular ( - grain orientation) to the solidification direction indicates that their superelastic strain, transformation strain, elastic modulus, transformation platform slope, and critical stress have obvious tension–compression asymmetry.

Efficient electricity production coupled with water treatment via a highly adaptable, successive water-energy synergistic system

There is an urgent need for sustainable sources of both energy and clean water. Herein, a novel highly efficient, cost-effective, scalable, adaptable and successive water-energy synergistic system (WESS) is developed using in-series flexible and permeable photocatalytic cell (PC) units for electricity production coupled with water treatment. Each PC unit is assembled as a monolithic device by integrating a Ti-mesh-based, high length-diameter ratio, single crystalline, 3–D anatase TiO2 nanowire array as a photoanode, a low-cost nylon net as a separator, and a carbon felt with improved surface graphitization and graphitic N as an efficient oxygen reduction reaction cathode. The WESS shows excellent energy recover and organic removal for different electrolyte concentrations, treatment capacities, substrate concentrations, and pollutant types. Notably, non-linear and marvellous improvements are achieved in both power output and organic degradation as the unit number increased. We attribute this behaviour to synergistic effects between the PC units, originating from the interactional potential in the serial system which accelerated the charge transfer of photoanode and electrode/electrolyte interface. In this case, a nine-unit WESS successively removed >99.8% of methyl orange accompanying with a maximum power density (Pmax) of ~10.53 mW cm−2, which was ~120 times as great as the highest Pmax of a photo-fuel-cell reported to date. This system also exhibited outstanding stability in long-term implementations. Moreover, efficient electricity generation and organic removal were achieved for the WESS under real sunlight and with an input of salty/seawater. The present novel strategy will pave the way for further systematic design of water-energy nexus techniques in clean energy production and wastewater resource utilization fields.

Adsorption, aggregation and sedimentation of titanium dioxide nanoparticles and nanotubes in the presence of different sources of humic acids.

Environmental behavior, bioavailability and risks posed by TiO2, nanomaterials (TiO2 NMs) in surface waters are affected by morphologies of the particles and geochemistry, including pH, inorganic and organic matter. Here, the adsorption, aggregation and sedimentation of TiO2 nanoparticles (TiO2 NPs) and nanotubes (TiO2 NTs) were investigated in the presence of Elliott Soil humic acid (HAE) and Suwannee River humic acids (HAS). The adsorption amount of HA on TiO2 NMs was inversely proportional to pH of solution. Maximum adsorption amount of HA on the surface of TiO2 NMs follows the order TiO2 NPs + HAE (236.05 mg/g) > TiO2 NTs + HAE (146.05 mg/g) > TiO2 NTs + HAS (70.66 mg/g) > TiO2 NPs + HAS (37.48 mg/g). Stability of TiO2 NPs and TiO2 NTs largely depended on their isoelectric point, morphology and solution pH in the absence of HA. Dispersion of TiO2 NMs was enhanced with solution pH deviated from the isoelectric point of nanomaterials due to electrostatic repulsion. Moreover, tubular structures of TiO2 NTs with higher length-diameter ratio seem to aggregate more easily than dose sphere-like TiO2 NPs. This might be due to their spherical structure enhancing steric repulsion. Notably, the adsorption of HA led to disagglomeration and significant stability of TiO2 NPs and TiO2 NTs due to steric hindrance under varying solution pH. In addition, adsorption time, concentration and sources of HA also influenced suspension/sedimentation behavior of TiO2 NPs and TiO2 NTs, and aromatic-rich HAE stabilized TiO2 NMs suspension more aggressively than aliphatic-rich HAS.