A Schiff base/quaternary ammonium salt bifunctional graphene oxide as an efficient adsorbent for removal of Th(IV)/U(VI)

Thiazole-Based Silver Ion Sensor for Sequential Colorimetric Visualization of Epinephrine in the Brain Tissues of an Alzheimer's Disease Model of Mouse

A thiazole-based probe, N'-((2-aminothiazol-5-yl)methylene)benzohydrazide (TBH), has been efficiently synthesized and characterized for the selective and sensitive detection of the neurotransmitter epinephrine (EP). The sensing strategy is based on the use of TBH for sequential colorimetric sensing of Ag+ and EP via in situ formation of Ag nanoparticles (Ag NPs) from the TBH-Ag+ complex. The generated Ag NPs lead to a bathochromic shift in absorption maximum and a change in color of the solution from light brown to reddish brown. TBH-Ag+ shows remarkable selectivity toward EP versus other drugs, common cations, anions, and some biomolecules. Moreover, TBH-Ag+ has a low detection limit for EP at 1.2 nM. The coordination of TBH-Ag+ has been proposed based on Job's plot, Fourier transform infrared spectroscopy (FT-IR), high-resolution mass spectrometry (HRMS), 1H NMR titration, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray analysis (EDAX), and density functional theory (DFT) studies. The composition and morphology of the generated Ag NPs have been analyzed by XPS, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The proposed sensing mechanism for EP has been supported by XPS of Ag after the reaction. Further, the sensitivity of TBH-Ag+ toward EP in brain tissues of an Alzheimer's disease model of mouse has been evaluated. A thorough comparison was done for evaluation of the proposed method.

Schiff base functionalized dialdehyde starch for enhanced removal of Cu (II): Preparation, performances, DFT calculations

Dialdehyde starch modified by 2-hydrazinopyridine (HYD-DAS) based on the reaction of dialdehyde starch (DAS) and 2-hydrazinopyridine was synthesized and characterized by FT-IR spectra, element analysis and SEM. HYD-DAS can efficiently adsorb Cu (II) ion to demonstrate visual color changes from yellow to dark brown in aqueous solutions. The influence on HYD-DAS to Cu (II) adsorption including pH value of solution, isotherm, kinetics, thermodynamics and possible mechanism had also been examined. Batch experiments indicate that HYD-DAS's to Cu (II) adsorption reaches equilibrium within 250 min, and its adsorption capacity and rate are 195.75 mg/g and 98.63 %, respectively. Moreover, HYD-DAS to Cu (II) adsorption remains robust and underscoring after five cycles to exhibit good selectivity and reusability. Kinetics studies suggest the absorption process follows a quasi-second-order with isotherms aligning to the Langmuir monolayer model, and thermodynamics reveals that it is a spontaneous endothermic nature of adsorption. Based on the analyses of XPS and DFT calculations, a possible mechanism for HYD-DAS to Cu (II) adsorption is that Cu (II) combined with nitrogen atoms from Schiff base and hydrazine pyridine ring in HYD-DAS.

Elimination of Pharmaceutical Compounds from Aqueous Solution through Novel Functionalized Pitch-Based Porous Adsorbents: Kinetic, Isotherm, Thermodynamic Studies and Mechanism Analysis

The long-term presence of PPCPs in the aqueous environment poses a potentially significant threat to human life and physical health and the safety of the water environment. In our previous work, we investigated low-cost pitch-based HCP adsorbents with an excellent adsorption capacity and magnetic responsiveness through a simple one-step Friedel-Crafts reaction. In this work, we further investigated the adsorption behavior of the prepared pitch-based adsorbents onto three PPCP molecules (DFS, AMP, and antipyrine) in detail. The maximum adsorption capacity of P-MPHCP for DFS was 444.93 mg g-1. The adsorption equilibrium and kinetic processes were well described through the Langmuir model and the proposed secondary kinetic model. The negative changes in Gibbs free energy and enthalpy reflected that the adsorption of HCPs onto PPCPs was a spontaneous exothermic process. The recoverability results showed that the adsorption of MPHCP and P-MPHCP onto DFS remained above 95% after 10 adsorption-desorption cycles. The present work further demonstrates that these pitch-based adsorbents can be used for multiple applications, which have a very extensive practical application prospect.

Network-Polymer-Modified Superparamagnetic Magnetic Silica Nanoparticles for the Adsorption and Regeneration of Heavy Metal Ions

Superparamagnetic magnetic nanoparticles (MNPs, Fe3O4) were first synthesized based on a chemical co-precipitation method, and the core-shell magnetic silica nanoparticles (MSNPs, Fe3O4@SiO2) were obtained via hydrolysis and the condensation of tetraethyl orthosilicate onto Fe3O4 seed using a sol-gel process. Following that, MSNPs were immobilized using a three-step grafting strategy, where 8-hloroacetyl-aminoquinoline (CAAQ) was employed as a metal ion affinity ligand for trapping specific heavy metal ions, and a macromolecular polymer (polyethylenimine (PEI)) was selected as a bridge between the surface hydroxyl group and CAAQ to fabricate a network of organic networks onto the MSNPs' surface. The as-synthesized MSNPs-CAAQ nanocomposites possessed abundant active functional groups and thus contained excellent removal features for heavy metal ions. Specifically, the maximum adsorption capacities at room temperature and without adjusting pH were 324.7, 306.8, and 293.3 mg/g for Fe3+, Cu2+, and Cr3+ ions, respectively, according to Langmuir linear fitting. The adsorption-desorption experiment results indicated that Na2EDTA proved to be more suitable as a desorbing agent for Cr3+ desorption on the MSNPs-CAAQ surface than HCl and HNO3. MSNPs-CAAQ exhibited a satisfactory adsorption capacity toward Cr3+ ions even after six consecutive adsorption-desorption cycles; the adsorption efficiency for Cr3+ ions was still 88.8% with 0.1 mol/L Na2EDTA as the desorbing agent. Furthermore, the MSNPs-CAAQ nanosorbent displayed a strong magnetic response with a saturated magnetization of 24.0 emu/g, and they could be easily separated from the aqueous medium under the attraction of a magnet, which could facilitate the sustainable removal of Cr3+ ions in practical applications.

Synthesis of novel magnetic pitch-based hypercrosslinked polymers as adsorbents for effective recovery of Ag+ with high selectivity

Silver is an important precious metal with superior ductility, electrical and thermal conductivity, photosensitivity, and antibacterial properties. However, without proper recycling and treatment, silver emissions may pose a threat to the human health and subsistence environment due to their toxicity. Therefore, it is environmentally and economically important to recover Ag from waste electronic equipment and anode slime. Herein, carboxyl functionalized modified magnetic nanoparticles (Fe₃O₄@3-phenylglutaricacid nanoparticles) were designed and prepared to obtain the low-cost magnetic pitch-based HCP adsorbents (MPHCP and P-MPHCP). The novelty of present work is that superior adsorption capacity and magnetic responsiveness of adsorbent can be obtained by a simple one-step Friedel-Crafts reaction with very low-cost raw material. The maximum Ag⁺ adsorption capacity of MPHCP and P-MPHCP were 321 and 353 mg/g, respectively. The adsorption was completed within a short duration of 15 min for MPHCP and P-MPHCP at an initial Ag⁺ concentration of 100 mg/L. Moreover, the most selective is P-MPHCP wherein Ag⁺ is α = 61 times more selective than Pb²⁺ at a concentration of 100 mg/L.The adsorption capacity of MPHCP and P-MPHCP towards Ag⁺ still maintains above 89% after ten cycles of adsorption-desorption. This study not only provides new guidance for the development of porous polymeric adsorbents but also provides technical feasibility for the field of recovery and reutilization of precious metals, which has a very extensive practical application prospect.

An elastic MOF/graphene aerogel with high photothermal efficiency for rapid removal of crude oil

Due to the frequent spill accidents during crude oil exploration and transport, to rapidly cleanup crude oil and eliminate the environmental pollution of oil spill is in high demand. In this work, a three-dimensional graphene aerogel (MEGA) with high elasticity, photothermal conversion capacity and adsorption capacity was prepared for rapid removal of crude oil. The results showed that the as-prepared MEGA exhibited a layered structure, the octahedral HKUST-1 nanoparticles and hydrophobic polydimethylsiloxane (PDMS) coatings were uniformly deposited on the surface. Such a hierarchical micro-nano porous structure not only improved the aerogel's hydrophobicity (water contact angle in air up to 152.7°), but also endowed it with strong oil adsorption capacity (41-118 times of its own weight). Especially, the MEGA showed excellent photothermal conversion capacity. Under light irradiation, its temperature raised to 80 ℃ from room temperature in 100 s. As a result, the adsorption for one drop of crude oil by MEGA was shortened from 5 h to 40 s, comparing with that in dark condition. In addition, the MEGA showed remarkable elasticity and mechanical stability, it could maintain more than 90% efficiency after 10 adsorption-compression cycles. This study suggests that the prepared MEGA has great potential for rapid removal of crude oil.

One-pot preparation of magnetic nitrogen-doped porous carbon from lignin for efficient and selective adsorption of organic pollutants

Organic pollutants pose a serious threat to water environment, thus it is essential to develop high-performance adsorbent to remove them from wastewater. Herein, nitrogen-doped magnetic porous carbon (M-PLAC) with three-dimensional porous structure was synthesized from lignin to adsorb methylene blue (MB) and tetracycline (TC) in wastewater. The calculated equilibrium adsorption amount by M-PLAC for MB and TC was 645.52 and 1306.00 mg/g, respectively. The adsorption of MB and TC on M-PLAC conformed to the pseudo-second-order kinetic model. The removal of MB by M-PLAC showed fast and efficient characteristics and exhibited high selectivity for TC in a binary system. In addition, M-PLAC was suitable for a variety of complex water environments and had good regeneration performance, demonstrating potential advantages in practical wastewater treatment. The organic pollutant adsorption by M-PLAC was attributed to electrostatic interaction, hole filling effect, hydrogen bonding, and the π-π interaction.

Selective adsorption of heavy metals from water by a hyper-branched magnetic composite material: Characterization, performance, and mechanism

The development of adsorbents to remove heavy metal ions from water with recyclable, high adsorption capacity, strong selectivity, safe, and economic performances has always been the focus and challenge of current research. A hyper-branched magnetic composite material (Fe₃O₄@SiO₂-S₄) was fabricated by a method combining "grafting,", "branching," and "modification,", and the structure was characterized by FTIR, XRD, SEM, TEM, SAED, VSM, TGA, and BET. In addition, the adsorption performance and mechanism for heavy metal ions in water were studied. The as-prepared composite material had excellent selective absorbability for Hg²⁺, Cd²⁺, and Ag⁺ in the presence of Fe³⁺, Fe²⁺, Cu²⁺, Mn²⁺, CO²⁺, Zn²⁺, and Ni²⁺, and when pH = 6, T = 30 °C, t = 4 h, it reached a saturated adsorption capacity of 2.42, 2.18, and 1.94 mmol/g to Hg²⁺, Cd²⁺, and Ag⁺, respectively. The adsorption isotherm was consistent with the Langmuir isotherm adsorption model, and the Dubinin Redushcke (D-R) model identified that the adsorption was chemical adsorption in nature. The adsorption kinetic followed the pseudo-second-order model and Boyd film diffusion models. The adsorption capacity of as-prepared material remained about 83% after five elutions. The adsorption mechanism and selective adsorption were revealed by FTIR, EDS, XPS, and DFT calculation. N atoms and O atoms of the active functional groups complexed with metal ions to form stable 2 heptachate chelates and 1 tridentate chelate to achieve the effect of adsorption; furthermore, the adsorption was mainly governed by N atoms of Schiff base groups. This work not only explored an innovative method for the construction of adsorbing materials but also provided a promising adsorbent to selectively remove heavy metal ions in water with potential application.

Function of Graphene Oxide as the “Nanoquencher” for Hg2+ Detection Using an Exonuclease I-Assisted Biosensor

Graphene oxide is well known for its excellent fluorescence quenching ability. In this study, positively charged graphene oxide (pGO25000) was developed as a fluorescence quencher that is water-soluble and synthesized by grafting polyetherimide onto graphene oxide nanosheets by a carbodiimide reaction. Compared to graphene oxide, the fluorescence quenching ability of pGO25000 is significantly improved by the increase in the affinity between pGO25000 and the DNA strand, which is introduced by the additional electrostatic interaction. The FAM-labeled single-stranded DNA probe can be almost completely quenched at concentrations of pGO25000 as low as 0.1 μg/mL. A simple and novel FAM-labeled single-stranded DNA sensor was designed for Hg²⁺ detection to take advantage of exonuclease I-triggered single-stranded DNA hydrolysis, and pGO25000 acted as a fluorescence quencher. The FAM-labeled single-stranded DNA probe is present as a hairpin structure by the formation of T–Hg²⁺–T when Hg²⁺ is present, and no fluorescence is observed. It is digested by exonuclease I without Hg²⁺, and fluorescence is recovered. The fluorescence intensity of the proposed biosensor was positively correlated with the Hg²⁺ concentration in the range of 0–250 nM (R² = 0.9955), with a seasonable limit of detection (3σ) cal. 3.93 nM. It was successfully applied to real samples of pond water for Hg²⁺ detection, obtaining a recovery rate from 99.6% to 101.1%.

Nature-Inspired Polyethylenimine-Modified Calcium Alginate Blended Waterborne Polyurethane Graded Functional Materials for Multiple Water Purification

In recent years, natural disasters such as hurricanes and floods have become more frequent, which usually leads to the pollution of drinking water. Drinking contaminated water may cause public health emergencies. The demand for healthy drinking water in disaster-affected areas is huge and urgent. Therefore, it is necessary to develop a simple water treatment technology suitable for emergencies. Inspired by nature, a fractional spray method was used to prepare graded purification material under mild conditions. The material consists of a calcium alginate isolation layer and a functional layer composed of calcium alginate, polyethylenimine, and water-based polyurethane, which can purify complex pollutants in water such as heavy metals, oils, pathogens, and micro/nano plastics through percolation. It does not require additional energy and can purify polluted water only under gravity. A disposable paper cup model was also designed, which can be used to obtain purified water by immersing in polluted water directly without other filtering devices. The test report shows that the water obtained from the paper cup was deeply purified. This design makes the material user-friendly and has the potential as a strategic material. This discovery can effectively improve the safety of drinking water after disasters and improve people's quality of life.

An Overview of Functionalized Graphene Nanomaterials for Advanced Applications

Interest in the development of graphene-based materials for advanced applications is growing, because of the unique features of such nanomaterials and, above all, of their outstanding versatility, which enables several functionalization pathways that lead to materials with extremely tunable properties and architectures. This review is focused on the careful examination of relationships between synthetic approaches currently used to derivatize graphene, main properties achieved, and target applications proposed. Use of functionalized graphene nanomaterials in six engineering areas (materials with enhanced mechanical and thermal performance, energy, sensors, biomedical, water treatment, and catalysis) was critically reviewed, pointing out the latest advances and potential challenges associated with the application of such materials, with a major focus on the effect that the physicochemical features imparted by functionalization routes exert on the achievement of ultimate properties capable of satisfying or even improving the current demand in each field. Finally, current limitations in terms of basic scientific knowledge and nanotechnology were highlighted, along with the potential future directions towards the full exploitation of such fascinating nanomaterials.

Preparation and characterization of polyimide membranes modified by a task-specific ionic liquid based on Schiff base for CO2/N2 separation

In order to increase CO₂/N₂ selectivity of polyimide (PI) dense membranes, task-specific ionic liquid (TSIL), 1-aminoethyl-3-buthylimidazolium hexafluorophosphate ([NH₂ebim][PF₆]), has been grafted to polymer chains as large side groups by forming the structure of Schiff base for the first time. The modified membranes were characterized by Fourier transform infrared spectroscopy (FT-IR), elemental analysis, thermogravimetric analysis (TGA), X-ray diffraction (XRD), dynamic thermomechanical analysis (DMA), and stress-strain testing. The results showed that TSIL had been successfully linked to PI chains by forming "C=N." The modified membranes had more free volume, which was favorable to the improvement of CO₂ permeability. The reduction of spin degree of freedom means the rigidity increment of polymer chains, which indicated that the selectivity of CO₂/N₂ can be enhanced. As a result, CO₂ permeability of the modified membrane (TSIL-0.8 wt%) was increased from 5.28 to 10.2 Barrer, and CO₂/N₂ selectivity was increased from 21.9 to 92.8 at 30 °C and 0.1 MPa. Meanwhile, the effects of different feed pressures (0.1-0.6 MPa) and different operating temperatures (30-60 °C) on CO₂/N₂ transport properties were also investigated, and it was found that the separation performances of the modified membranes had already exceeded Robeson's upper bound.

Epoxy graphene oxide from a simple photo-Fenton reaction and its hybrid with phytic acid for enhancing U(VI) capture

A novel approach to synthesize phytic acid (PA) functionalized graphene oxide (P-pFGO-7) treated by the photo-Fenton reaction has been designed, which has been used as an adsorbent for efficient capture of U(VI) from aqueous solution. The structure and morphology of P-pFGO-7 were characterized well. The adsorption property for P-pFGO-7 was comprehensively assessed by batch experiments, showing the high adsorption capacity (266.7 mg/g, at pH = 4.0, T = 298 K), fast adsorption kinetics (~10 min), good selectivity for U(VI) and Ln-An ions in various coexisting ions and excellent regeneration capacity. With the assistance of various characterization techniques and batch adsorption results, it is found that PA makes the most contribution to coordinate U(VI) heavily depending on the PO moiety. P-pFGO-7 could be regenerated by 0.1 mol/L Na₂CO₃ with ~95% desorption efficiency and reused well after five recycles. This present work provides a feasible route to modify graphene oxide and extend PA for potentially practical application in the removal of U(VI) from radioactive wastewater.

Comparative adsorption capabilities of rubbish tissue paper-derived carbon-doped MgO and CaCO3 for EBT and U(VI), studied by batch, spectroscopy and DFT calculations

Water pollution due to organic dyes and radionuclides is a challenging issue to the modern world. Cheap and efficient adsorbents are needed for their removal from wastewaters. Carbon-doped magnesium oxide (C-MgO) and calcium carbonate (C-CaCO₃) were synthesized by the in situ hydrothermal treatment of Mg(OH)₂ and Ca(OH)₂ with carbon, and applied for the removal of eriochrome black T (EBT) at pH = 2.0 and uranium (U(VI)) at pH = 6.0. The Langmuir monolayer adsorption capacities of C-MgO (3.62 × 10^-4 mol/g for EBT and 8.10 × 10^-4 mol/g for U(VI)) were higher than those of C-CaCO₃ (2.53 × 10^-4 mol/g for EBT and 5.92 × 10^-4 mol/g for U(VI)). The high adsorption capacity of C-MgO was also evidenced with DFT calculations which showed that the sorption energies (ΔE) of C-MgO for EBT (20.62 kcal/mol) and U(VI) (63.41 kcal/mol) were higher than those of C-CaCO₃ for EBT (10.21 kcal/mol) and U(VI) (34.29 kcal/mol). In all cases, the electrostatic interactions were involved in the adsorption process. The sorption kinetic data followed pseudo-second-order kinetics. The results demonstrate that both C-MgO and C-CaCO₃ are reusable and can be effectively applied for the elimination of EBT and U(VI) from wastewater.

Porous biochar modified with polyethyleneimine (PEI) for effective enrichment of U(VI) in aqueous solution

This study investigated the modification of moso bamboo biochar with polyethyleneimine (PEI) for the efficient enrichment of U(VI) in aqueous solution. The alkali/acid treated biochars with amine groups (PEI-alkali-biochar or PEI-acid-biochar) were characterized by SEM, BET, TGA, FTIR and XPS. The effects of contact time, U(VI) concentration, pH and ionic strength on U(VI) adsorption by PEI-alkali/acid-biochar were studied. U(VI) adsorption process on PEI-alkali/acid-biochar obeys pseudo-second-order model. Intraparticle diffusion model was used to investigate the controlled factors of the adsorption process. The fitting of Langmuir model gives the maximum adsorption capacities of 212.7 mg/g for PEI-alkali-biochar and 185.6 mg/g for PEI-acid-biochar, which are almost 9-10 times higher than that of pristine biochar (20.1 mg/g). The thermodynamic parameters illustrate that U(VI) adsorption on PEI-alkali/acid-biochar is an exothermic and spontaneous process. The FTIR and XPS analyses imply that U(VI) adsorption by PEI-alkali/acid-biochar is mainly controlled by complexation between U(VI) and amine groups. PEI-alkali/acid-biochar could be considered as a low-cost and outstanding material for U(VI) removal from radionuclide wastewater in practical application.

Antimicrobial Efficiency and Surface Interactions of Quaternary Ammonium Compound Absorbed on Dielectric Barrier Discharge (DBD) Plasma Treated Fiber-Based Wiping Materials

The physicochemical interactions between alkyldimethylbenzylammonium chloride (ADBAC) as disinfectant and three commercial wiping materials made from 100% polyester (PET), 55%cellulose/45%PET (blend), and 100% cellulose were investigated after treatment with dielectric barrier discharge (DBD) plasma at atmospheric pressure. Wipe material type in terms of cellulose content, liquor ratio, and immersion time demonstrated a significant influence on the adsorption of ADBAC. The higher the content of cellulose in the material, the higher is the adsorption of ADBAC active ingredient. The antimicrobial tests confirm that the ADBAC adsorbed on pure cellulosic material is inactivated losing its bactericidal activity, while 100% PET and blend wipes showed good antimicrobial efficacy. XPS analysis demonstrates the strong interactions of ADBAC with the plasma-generated oxygen species in the polyester-containing wipes surface. Unexpectedly, plasma-treated blend wipe displays a reverse antimicrobial effect compared to untreated samples, performing better in Gram-negative bacteria. The best result was obtained in the plasma treated 100% polyester wipe showing an improvement of about 20% in Gram-positive bacteria and an excellent performance in Gram-negative ones. This method allows the unprecedented use of pure polyester as effective wiping material for surface disinfection eliminating the major drawback of pure polyester, its high hydrophobicity.

Benzotriazole decorated graphene oxide for efficient removal of U(VI)

There is a need to develop highly efficient materials for capturing uranium from nuclear wastewater. Here, 5-methylbenzotriazole modified graphene oxide (MBTA-GO) was used to adsorb U(VI) from aqueous solution. By the trials of different conditions, we found that the removal of U(VI) from acidic solution was strongly dependent on pH but independent of ionic strength. The U(VI) adsorption was perfectly conformed to the pseudo-second-order kinetics and the adsorption isotherms were simulated by the Langmuir model well. A high removal capacity (q_max = 264 mg/g) for U(VI) at pH 3.5 was obtained. XPS, EXAFS analyses and DFT calculations revealed that the mechanism of uranium capture was ascribed to (i) the surface complexation by benzotriazole and carboxyl groups (providing lone pair electrons) on MBTA-GO and (ii) enhanced synergistic coordination ability of delocalized π-bond of triazole group toward U due to the transfer of electrons from graphene sheet to benzotriazole. DFT calculations further demonstrated that benzotriazole displayed stronger binding with U(VI) compared to carboxyl group due to higher binding energy of [Side/Surface-U-MBTA-GO] (79.745, 54.986 kcal/mol) than [MBTA-GO-COOH-U] (27.131 kcal/mol). This work will provide valuable insight into designing novel nitrogen-containing adsorbents for practical application in wastewater treatment.

A novel magnetite nanorod-decorated Si-Schiff base complex for efficient immobilization of U(vi) and Pb(ii) from water solutions

A novel silicon Schiff base complex (Si-SBC) and magnetite nanorod-decorated Si-SBC (M/SiO2-Si-SBC) were synthesized and well characterized in detail. The synthesized materials were applied for the removal of U(vi) and Pb(ii) from water solutions under various experimental conditions. The monolayer maximum adsorption capacities of M/SiO2-Si-SBC (6.45 × 10-4 mol g-1 for Pb(ii) and 4.82 × 10-4 mol g-1 for U(vi)) obtained from the Langmuir model at 25 °C and pH = 5.00 ± 0.05 were higher than those of Si-SBC (5.18 × 10-4 mol g-1 for Pb(ii) and 3.70 × 10-4 mol g-1 for U(vi)). Moreover, DFT calculations showed that the high adsorption energies (Ead) of 7.61 kcal mol-1 for Pb2+-(Si-SBC) and 2.72 kcal mol-1 for UO22+-(Si-SBC) are mainly attributed to stronger electrostatic interactions. The results revealed that the Si-SBC and M/SiO2-Si-SBC could be used as efficient adsorbents for the effective elimination of U(vi) and Pb(ii) from contaminated wastewater. High sorption capacity and reusability indicated the practical applications of the synthesized materials in environmental pollution cleanup.