Adsorption Of Platinum Research Articles

Evaluation of activated carbon and bio-polymer modified activated carbon performance for palladium and platinum removal

Because of the increase in needs for platinum group metals, as well as their low availability in nature and their environmental concerns, it is getting more urgent to separation and recovers them from dilute solutions. In this research, commercial activated carbon was used to optimize the palladium and platinum removal by applying the Taguchi approach. According to the results, the optimum operating conditions for palladium and platinum removal by activated carbon were pH=2, particle size of adsorbent=0.21mm and adsorbent dose=10g/L. Under these optimum operating conditions, more than 98% of palladium and platinum were removed by activated carbon in 3h. The equilibrium adsorption data were well described by the Langmuir and Freundlich models. While commercial activated carbon had the palladium and platinum adsorption capacity of 35.7 and 45.5mg/g, respectively, the bio-polymer modified activated carbon was able to adsorb 43.5 and 52.6mg/g of palladium and platinum, respectively. It was observed that the adsorption kinetics of palladium and platinum on these adsorbents could be well analyzed with pseudo-second-order model.

Improved adsorption and separation of palladium(II) and platinum(IV) in strong hydrochloric acid solutions using thiocyanate‐retaining tannin gel

AbstractA tannin gel (TG) synthesized from condensed tannin molecules has a remarkable ability to adsorb various metal ions in aqueous solutions. In the present study, we have investigated the adsorption behaviors of palladium and platinum ions, Pd(II) and Pt(IV), in strong HCl solutions using the thiocyanate‐retaining tannin gel (SCN‐TG) prepared by adsorption of thiocyanate ion (SCN−) onto the TG in acidic thiocyanate solutions as reported previously (Ind Eng Chem Res 2011, 50, 12366). Although the adsorption rate of Pt(IV) is slow compared to that of Pd(II), the SCN‐TG was able to adsorb both Pd(II) and Pt(IV) in a 1 M HCl solution, where the TG can never adsorb them. Besides, we have succeeded in the selective adsorption of Pd(II) from the mixture solution of Pd(II) and Pt(IV) at a temperature somewhat lower than room temperature using the SCN‐TG. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Thermal stability of new sorption materials based on polysiloxanes

The thermal stability of the unmodified, aminated, and thiocarbamoylated polysiloxanes has been studied. The siloxane matrix is stable in the temperature range up to 800°C. For the first time, mass spectrometry has been applied to the analysis of the composition of the gaseous products of thermal decomposition of the studied polysiloxanes. It has been shown that, in the process of thermal decomposition, the terminal functional groups are detached and oxidized. Water, ammonia, nitrogen, carbon, and sulfur (in the case of thiourea-modified sorbent) oxides are formed predominantly. The quantitative removal of functional groups during heating up to 800°C has been confirmed by IR spectroscopy. A mechanism of thermal decomposition of polysiloxane xerogels has been proposed. It has been found that adsorption of platinum increases the thermal stability of the samples.

Density functional and bonding study of hydrogen and platinum adsorption on B2-FeTi (111) slab

We performed a density functional theory study (DFT) of hydrogen interaction with Pt on the B2-FeTi (111) surface. The DFT is employed to trace the relevant orbital interactions and to discuss the electronic changes of incorporating H on the Fe–Ti bonding. We determined the optimal location for Pt and then for adsorbed hydrogen. We also followed the density of states and the changes in the chemical bonding for both adsorbed atoms on the surface. The overlap population analysis reveals metal–metal bond breaking after hydrogen adsorption, being this bond the more affected.

Platinum recovery from dilute platinum solutions using activated carbon

Platinum adsorption on activated carbon, a common adsorbent, from dilute platinum-containing solution of 57.6 mg/L was investigated. The effects of different adsorption parameters on the platinum adsorption were reported in detail. The percentage of platinum adsorption increased with increasing the amount of adsorbent, as well as with increasing contact time and temperature. A platinum adsorption of 75% was obtained using 400 mg of activated carbon at a shaking rate of 200 r/min for 3 h at 25 °C. A platinum adsorption of 88%, however, was obtained at 80 °C using 200 mg of activated carbon within only 1 h, which indicates that temperature plays a vital role in the adsorption process. A platinum adsorption of 99% or above was attained using 400 mg of activated carbon after contact for 3 h at 80 °C.

Recovery of platinum, tin and indium from spent catalysts in chloride medium using strong basic anion exchange resins

This work describes a route for platinum recovery from spent commercial Pt and PtSnIn/Al 2O 3 catalysts using strong basic mesoporous and macroporous anion exchange resins (Cl − form). The catalysts were leached with aqua regia (75 °C, 20–25 min). Platinum adsorption was influenced by the presence of other metals which form chlorocomplexes (tin, indium) and also base metals (aluminum). However, it was possible to overcome this fact by a sequential desorption procedure. Aluminum was selectively removed from the resins by elution with 3 mol L −1 HCl. Platinum was desorbed passing 1 mol L −1 Na 2S 2O 3 (pH 9). Tin was removed by elution with 0.1 mol L −1 ascorbic acid. Indium was removed using 0.1 mol L −1 EDTA as eluent. Desorption efficiency exceeded 99% for all metals. Metals were recovered in high yields (>98 wt%).

Adsorption of Single Platinum Atom on the Graphene Oxide: The Role of the Carbon Lattice

We present the density functional calculations for the adsorption of a single platinum (Pt) atom on the 2-fold bridged-oxygen (Ob) covered graphene (graphene oxide, GO). We found the incoming Pt at low kinetic energies prefers to interact with only one Ob and the reaction weakens the coupling of the Ob with the underlying two carbon atoms to give rise to an upward tilted Pt–Oa configuration with the Oa singly connected to one of the underlying carbon (C1L) and leaving a semifilled and lone-paired orbital on the other carbon (C*). The highly reactive and long-lived C* plays an important role determining the energy barriers and branching nature of the subsequent reaction pathways. By being long-lived, reactions of the C* spilt into the early- and late-C* pathways depending when the long-lived C* is participated in the reaction. The early-C* pathways involve direct reactions of the C* with either the Pt or the neighboring carbons with low energy barriers (Ea < 0.3 eV) and give rise to stable local minimum st...

Aged Nano-Structured Platinum Based Catalyst: Effect of Chemical Treatment on Adsorption and Catalytic Activity

To examine the effect of chemical treatment on the adsorption and catalytic activity of nanostructured platinum based catalyst, the aged commercial Pt/AC catalyst was pretreated with sulfuric acid (H2SO4) and a cleaning agent (Hexane). Several reliable methods such as nitrogen adsorption, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and inductively coupled plasma (ICP) were employed to characterize the aged Pt/AC catalyst and its chemically pretreated Pt/AC catalysts. The catalytic and adsorption activities of nano-structured heterogeneous Pt/AC catalyst were investigated on the basis of toluene oxidation and adsorption isotherm data. In addition, the adsorption isotherms of toluene were used to calculate the adsorption energy distribution functions for the parent catalyst and its pre-treated nano-structured Pt/AC catalysts. It was found that sulfuric acid aqueous treatment can enhance the catalytic performance of aged Pt/AC catalyst toward catalytic oxidation of toluene. It was also shown that a comparative analysis of the energy distribution functions for nano-structured Pt/AC catalysts as well as the pore size distribution provides valuable information about their structural and energetic heterogeneity.

Erratum to “Adsorption and surface complexation modeling of palladium, rhodium and platinum in surficial semi-arid soils and sediments” [Appl. Geochem. 24(1), 86–95

Erratum to “Adsorption and surface complexation modeling of palladium, rhodium and platinum in surficial semi-arid soils and sediments” [Appl. Geochem. 24(1), 86–95

Adsorption of platinum(IV) and palladium(II) from aqueous solution by magnetic cross-linking chitosan nanoparticles modified with ethylenediamine

The adsorption characteristics of platinum(IV) and palladium(II)from aqueous solutions onto the ethylenediamine-modified magnetic chitosan nanoparticles (EMCN) have been investigated. The magnetic chitosan nanoparticles were prepared by adding the basic precipitant of NaOH solution into a W/O microemulsion system. The transmission electron microscope showed that the diameter of EMCN was from 15 to 40 nm. The adsorption experiments indicated that the maximum adsorption capacity occurred at around pH 2.0 for both Pt(IV) and Pd(II). Due to the small diameter and the high surface reactivity, the adsorption equilibrium of Pt(IV) and Pd(II) onto the EMCN reached very quickly. The maximum loading capacity of EMCN for Pt(IV) and Pd(II) was determined to be 171 and 138 mg/g, respectively. Sorption isotherms were determined both in single component with pure metal solutions and bicomponent systems with different Pd/Pt mass ratios. The results showed that the sorbents had a greater affinity for Pt(IV) than for Pd(II). The total sorption capacity was comparable to that of each metal individually, indicating that the metals compete for the same sorption sites. It was found that 0.4 M HNO 3–1.0 M thiourea solution provided effectiveness of the desorption of Pt(IV) and Pd(II) from EMCN, while 5 M ammonia exhibited the highest selectivity for the tested metal ions.

Adsorption of platinum(IV) and palladium(II) from aqueous solution by thiourea-modified chitosan microspheres

The chitosan microparticles were prepared using the inverse phase emulsion dispersion method and modified with thiourea (TCS). TCS was characterized by scanning electron microscope (SEM), the Fourier transform infrared (FT-IR) spectra, sulfur elemental analysis, specific surface area and pore diameter. The effects of various parameters, such as pH, contact time, initial concentration and temperature, on the adsorption of Pt(IV) and Pd(II) by TCS were investigated. The results showed that the maximum adsorption capacity was found at pH 2.0 for both Pt(IV) and Pd(II). TCS can selectively adsorb Pt(IV) and Pd(II) from binary mixtures with Cu(II), Pb(II), Cd(II), Zn(II), Ca(II), and Mg(II). The adsorption reaction followed the pseudo-second-order kinetics, indicating the main adsorption mechanism of chemical adsorption. The isotherm adsorption equilibrium was well described by Langmuir isotherms with the maximum adsorption capacity of 129.9 mg/g for Pt(IV) and 112.4 mg/g for Pd(II). The adsorption capacity of both Pt(IV) and Pd(II) decreased with temperature increasing. The negative values of enthalpy (Δ H°) and Gibbs free energy (Δ G°) indicate that the adsorption process is exothermic and spontaneous in nature. The adsorbent was stable without loss of the adsorption capacity up to at least 5 cycles and the desorption efficiencies were above 95% when 0.5 M EDTA–0.5 M H 2SO 4 eluent was used. The results also showed that the preconcentration factor for Pt(IV) and Pd(II) was 196 and 172, respectively, and the recovery was found to be more than 97% for both precious metal ions.

Continuous adsorption of Pt ions in a batch reactor and packed-bed column

Continuous adsorption of platinum (Pt) was performed by using a batch reactor and a packed-bed column system in which amine-treated activated carbon (AC) pellets (Norit RO 0.8) were used as adsorbents. The feed solution (pH 2.0) contained a mixture of Pt and base metal ions (Fe 2+, Cr 3+) in chloride media. The central focus of the study was directed at comparing selectivity and mass transfer characteristics of Pt ions in a batch reactor and packed-bed column. In a batch reactor, the AC particles were agitated mildly (500 rpm) within the bulk solution (810 mL) while fresh feed was fed (6 mL/min) to the reactor continuously in up flow mode. The ratio of AC mass to solution volume in the stirred batch reactor was kept constant (1 g: 810 mL) at ambient conditions. The mass transfer of Pt ions in the packed-bed column was evaluated by correlating the ratio of Sherwood and Schmidt numbers with Reynolds numbers. In the case of a batch reactor, the rate equation was integrated and then fitted to the adsorption data in order to determine the rate constants and mass transfer coefficients. Separation factors ( β Pt/Fe, β Pt/Cr), in the order of 10 2 were achieved in a packed-bed column. However, separation factors in a batch reactor were hundred-fold higher than packed-bed column values indicative of superior mass transfer of Pt in an agitated-carbon-in-liquid (ACIL) process.

A first-principles study of nitrogen- and boron-assisted platinum adsorption on carbon nanotubes

We have performed first-principles calculations to investigate the origin of adsorption of platinum on nitrogen- and boron-doped carbon nanotubes (CNTs). Our calculation results reveal that both nitrogen- and boron-doped CNTs can assist the reactivity of platinum adsorption on the CNT surface, although the detailed mechanisms are very different. For nitrogen-doped CNTs, the enhanced adsorption results from activation of the nitrogen-neighboring carbon atoms due to the large electron affinity of nitrogen. In this case, the nitrogen atoms mediate the platinum adsorption enhancement on the CNT surface. In contrast, the enhanced platinum adsorption in boron-doped CNTs can be attributed to the strong hybridization between the platinum d orbital and boron p orbital. Our results explain the experimentally observed enhanced adsorption of platinum on nitrogen-doped CNTs and also suggest that boron-doped CNTs may be a better candidate for fuel cell applications.

Adsorption and surface complexation modeling of palladium, rhodium and platinum in surficial semi-arid soils and sediment

Sorption isotherms, time-dependent adsorption and surface complexation modeling studies were used to investigate the post-depositional mobility of three of the platinum group-elements (Pd, Rh, and Pt) in semi-arid soil and sediment samples with varying surface properties. The acidity constants (Log K a1 and Log K a2 ), optimized from batch titration data, ranged from 4.69 to 5.34 for Log K a1 and from −6.51 to −7.61 for Log K a2 , suggesting the occurrence of both protonation and deprotonation reactions on the solid surfaces. Partition coefficients and removal rates of the metals had a general trend of Pd > Pt > Rh. The sediment sample, with the highest clay content and exchangeable cation concentrations, also had the highest affinity for the metals. The times required for sediment to adsorb 63% of the metals were 2.63 h, 4.08 h and 10.64 h for Pd, Pt and Rh, respectively. The FITEQL program successfully optimized the conditional binding constants of the metals on the solids from batch adsorption data. The constants decreased in the order of Pd > Rh > Pt, which was consistent with the observed high affinity of the solids for Pd. The modeling results also showed that aqueous Pd was the least sensitive to pH followed by Rh and Pt. However, metal adsorption below the points of zero net proton charges (ca. pH 6.7) is attributable to the involvement of permanent negatively charged binding sites in the adsorption process. Notably, partition coefficients, removal rates and conditional binding constants all showed a high affinity of Pd for the solids. A similarity between the model outputs and the batch adsorption data indicates the suitability of the model for describing the mobility and retention of the three metals in semi-arid soils and sediments.

Hybridized surface-plasmon resonances of platinum colloid-adsorbed gold nanospheres

The surface-plasmon resonances of gold nanospheres dispersed in water split into two bands and shift to the red with the adsorption of colloidal platinum. These spectral changes are quite different from both the calculated and the experimental spectral variations of gold nanospheres with the thickness of coating platinum. Thus, these spectral changes have been attributed to the elementary plasmon interactions of the core gold and the adsorbed colloidal platinum as well as to the modification of the medium refraction index of the gold nanospheres. A simple and intuitive picture has been drawn to describe the hybridization plasmon interactions of a platinum colloid-adsorbed gold nanosphere.

Adsorption of palladium, platinum, and gold chloride complexes by carbon fibers with various structures

Data are given characterizing the effects of the porous structures in activated carbon fibers (ACF) and the amounts of oxidized carbon forms on the extent and rate of adsorption for various chloride complexes of the platinum metals and gold. The adsorption mechanisms on ACF are considered for these metal chloride complexes. The practical significance of the research is considered.

Adsorption of platinum(IV) onto D301R resin

Pt(IV) was quantitatively adsorbed by D301R resin in the medium of pH = 3.47. The statically saturated adsorption capacity is 410 mg/g. Pt(IV) adsorbed on D301R resin can be eluted by 1.0-2.0 mol/L NaOH. The rate constant is k 298 = 5.43 × 10 −5S −1. The adsorption of Pt(IV) on D301R resin obeys the Freundlich isotherm. The adsorption parameters of thermodynamics are as follows: enthalpy change Δ H = 4.37 kJ/mol, Gibbs free energy change Δ G = −5.39 kJ/mol, and entropy change Δ S = 32.76 J/(mol·K). The apparent activation energy is E a = 22.5 kJ/mol. The coordination molar ratio of the functional group of D301R resin to Pt(IV) is 2:1.

Pt-induced structures on Si(1 1 0) studied by STM

The structures induced by platinum (Pt) adsorption on Si(1 1 0) surface have been studied by scanning tunneling microscopy (STM) for coverage up to 2 monolayers (ML). Three surface phases have been found to form: “ 5 × 4 ”, “ 13 × 2 ” and “ 6 × 5 ” for Pt coverages 0.3, 0.5 and 1 ML respectively. All structures are formed by one-dimensional rows aligned along the [ 1 1 ¯ 0 ] direction. At the coverage > 1 ML islands of, probably, Pt silicide start to form in form of 1D nanowires.

Surfactant Gel Adsorption of Platinum(II), (IV) and Palladium(II) as Chloro-complexes and Kinetic Separation of Palladium from Platinum Using EDTA

A micellar solution of cetylpyridinium chloride (CPC) can separate into two phases due to a temperature change or to the addition of salts. Platinum(II), (IV) and palladium(II) reacted with chloride ions to form stable anionic complexes of PtCl4(2-), PtCl6(2-) and PdCl4(2-), respectively, and were adsorbed onto the CPC gel phase. The CPC phase plays the role of an ion-exchange adsorbent for the anionic complexes. By such a procedure, the precious metals of platinum and palladium could be separated from base metals such as copper, zinc and iron. The kinetic separation was performed by a ligand exchange reaction of the palladium(II) chloro-complex with EDTA at 60 degrees C. The anionic palladium(II)-EDTA complex could not bind the opposite charged CP+ and was desorbed from the CPC phase. In the aqueous phase, the recovery of palladium(II) by the double-desorption was 101.1 +/- 1.2%. The platinum(II) and (IV) chloro-complexes were stable for at least 30 min and remained in the CPC phase.

First-principles study of thePt∕CeO2(111)interface

The adsorption of platinum on the ceria (111) surface may change the reduction and redox properties of $\mathrm{Ce}{\mathrm{O}}_{2}$. The density functional theory with the inclusion of on-site Coulomb interaction has been used to study the properties of Pt adsorbed on the (111) surfaces of stoichiometric and reduced ceria. In all cases, strong interactions are found between the Pt and the surfaces. The Pt-O-Ce bonds may be formed between the Pt adatom and the surface in the preferred adsorption mode. The adsorption on the reduced surface is stronger than on the unreduced surface. The formation energy of an O vacancy at the $\mathrm{Pt}∕\mathrm{Ce}{\mathrm{O}}_{2}(111)$ interface is lower than on the clean $\mathrm{Ce}{\mathrm{O}}_{2}(111)$ surface due to the existence of the lower lying partially occupied metal induced gap states including mainly the $\mathrm{Pt}\phantom{\rule{0.2em}{0ex}}4d$ states below the empty $\mathrm{Ce}\phantom{\rule{0.2em}{0ex}}4f$ band.