OH Units Research Articles

Exploring polyelectrolytic features of the exudate from native Acacia nilotica for flocculating aqueous kaolin suspension

The air dried exudate of native Acacia nilotica, referred as natural gum or NG in this article, has been purified and characterized for using it as a local, bio-based flocculant for kaolin suspension. Results show that NG is a carbohydrate of nearly 25% purity out of which 7% is the reducing sugar and the rest 75% is natural silica present as contaminant. The macromolecule contains COOH units. This along with OH units impart polyelectrolytic character for which the molecules interact with SiOH units of kaolin and settles the suspension. The settling data shows that 25ppm is the best flocculant dose in respect of fastest settling and lowest residual turbidity for settling a 3wt% suspension. Investigation on pH shows that 1.6–2.6 is the best working range, however, in the high stability zone (low acidity to strong basicity), the results are satisfactory. Due to high average floc size and low effective density of the flocs obtained at high acidic condition, the amount of fresh water lost inside the sediment is higher as compared to neutral and basic conditions.

Infrared and Raman Spectroscopic Characterization of the Silicate Mineral Gilalite Cu5Si6O17 · 7H2O

ABSTRACT Gilalite is a copper silicate mineral with a general formula of Cu5Si6O17 · 7H2O. The mineral is often found in association with another copper silicate mineral, apachite, Cu9Si10O29 · 11H2O. Raman and infrared spectroscopy have been used to characterize the molecular structure of gilalite. The structure of the mineral shows disorder, which is reflected in the difficulty of obtaining quality Raman spectra. Raman spectroscopy clearly shows the absence of OH units in the gilalite structure. Intense Raman bands are observed at 1066, 1083, and 1160 cm−1. The Raman band at 853 cm−1 is assigned to the –SiO3 symmetrical stretching vibration and the low-intensity Raman bands at 914, 953, and 964 cm−1 may be ascribed to the antisymmetric SiO stretching vibrations. An intense Raman band at 673 cm−1 with a shoulder at 663 cm−1 is assigned to the ν4 Si-O-Si bending modes. Raman spectroscopy complemented with infrared spectroscopy enabled a better understanding of the molecular structure of gilalite.

The molecular structure of the phosphate mineral beraunite Fe2+Fe53+(PO4)4(OH)5⋅4H2O – A vibrational spectroscopic study

The mineral beraunite from Boca Rica pegmatite in Minas Gerais with theoretical formula Fe2+Fe53+(PO4)4(OH)5⋅4H2O has been studied using a combination of electron microscopy with EDX and vibrational spectroscopic techniques.Raman spectroscopy identifies an intense band at 990cm−1 and 1011cm−1. These bands are attributed to the PO43− ν1 symmetric stretching mode. The ν3 antisymmetric stretching modes are observed by a large number of Raman bands. The Raman bands at 1034, 1051, 1058, 1069 and 1084 together with the Raman bands at 1098, 1116, 1133, 1155 and 1174cm−1 are assigned to the ν3 antisymmetric stretching vibrations of PO43− and the HOPO32− units. The observation of these multiple Raman bands in the symmetric and antisymmetric stretching region gives credence to the concept that both phosphate and hydrogen phosphate units exist in the structure of beraunite. The series of Raman bands at 567, 582, 601, 644, 661, 673, and 687cm−1 are assigned to the PO43− ν2 bending modes. The series of Raman bands at 437, 468, 478, 491, 503cm−1 are attributed to the PO43− and HOPO32− ν4 bending modes.No Raman bands of beraunite which could be attributed to the hydroxyl stretching unit were observed. Infrared bands at 3511 and 3359cm−1 are ascribed to the OH stretching vibration of the OH units. Very broad bands at 3022 and 3299cm−1 are attributed to the OH stretching vibrations of water. Vibrational spectroscopy offers insights into the molecular structure of the phosphate mineral beraunite.

A Raman and infrared spectroscopic characterisation of the phosphate mineral phosphohedyphane Ca2Pb3(PO4)3Cl from the Roote mine, Nevada, USA

Phosphohedyphane Ca2Pb3(PO4)3Cl is rare Ca and Pb phosphate mineral that belongs to the apatite supergroup. We have analysed phosphohedyphane using SEM with EDX, and Raman and infrared spectroscopy. The chemical analysis shows the presence of Pb, Ca, P and Cl and the chemical formula is expressed as Ca2Pb3(PO4)3Cl. The very sharp Raman band at 975cm−1 is assigned to the PO43-ν1 symmetric stretching mode. Raman bands noted at 1073, 1188 and 1226cm−1 are to the attributed to the PO43-ν3 antisymmetric stretching modes. The two Raman bands at 835 and 812cm−1 assigned to the AsO43-ν1 symmetric stretching vibration and AsO43-ν3 antisymmetric stretching modes prove the substitution of As for P in the structure of phosphohedyphane. A series of bands at 557, 577 and 595cm−1 are attributed to the ν4 out of plane bending modes of the PO4 units. The multiplicity of bands in the ν2, ν3 and ν4 spectral regions provides evidence for the loss of symmetry of the phosphate anion in the phosphohedyphane structure. Observed bands were assigned to the stretching and bending vibrations of phosphate tetrahedra. Some Raman bands attributable to OH stretching bands were observed, indicating the presence of water and/or OH units in the structure.

A vibrational spectroscopic study of the phosphate mineral lulzacite Sr2Fe2+(Fe2+,Mg)2Al4(PO4)4(OH)10

The mineral lulzacite from Saint-Aubin des Chateaux mine, France, with theoretical formula Sr2Fe2+(Fe2+,Mg)2Al4(PO4)4(OH)10 has been studied using a combination of electron microscopy with EDX and vibrational spectroscopic techniques. Chemical analysis shows a Sr, Fe, Al phosphate with minor amounts of Ga, Ba and Mg. Raman spectroscopy identifies an intense band at 990cm−1 with an additional band at 1011cm−1. These bands are attributed to the PO43-ν1 symmetric stretching mode. The ν3 antisymmetric stretching modes are observed by a large number of Raman bands. The Raman bands at 1034, 1051, 1058, 1069 and 1084 together with the Raman bands at 1098, 1116, 1133, 1155 and 1174cm−1 are assigned to the ν3 antisymmetric stretching vibrations of PO43- and the HOPO32- units. The observation of these multiple Raman bands in the symmetric and antisymmetric stretching region gives credence to the concept that both phosphate and hydrogen phosphate units exist in the structure of lulzacite. The series of Raman bands at 567, 582, 601, 644, 661, 673 and 687cm−1 are assigned to the PO43-ν2 bending modes. The series of Raman bands at 437, 468, 478, 491, 503cm−1 are attributed to the PO43- and HOPO32-ν4 bending modes.No Raman bands of lulzacite which could be attributed to the hydroxyl stretching unit were observed. Infrared bands at 3511 and 3359cm−1 are ascribed to the OH stretching vibration of the OH units. Very broad bands at 3022 and 3299cm−1 are attributed to the OH stretching vibrations of water. Vibrational spectroscopy offers insights into the molecular structure of the phosphate mineral lulzacite.

Rhodium(III)‐Catalyzed Direct C‐2 Olefination of Unactivated Indoles Utilizing OH/NH2 as Directing Group

AbstractOxidative C‐2 olefination of indoles/pyrrole via rhodium(III)‐catalyzed direct CH bond activation is reported. Phenolic OH and aniline NH2 units were revealed to be effective chelating groups to activate the aryl CH bond. The reactions proceeded with excellent selectivity and high functional group tolerance, furnishing 2‐vinylindoles/2‐vinylpyrroles in good yields.magnified image

The N‐Alkylation of Sulfonamides with Alcohols in Water Catalyzed by the Water‐Soluble Iridium Complex {Cp*Ir[6,6′‐(OH)2bpy](H2O)}[OTf]2

AbstractThe water‐soluble iridium complex {Cp*Ir[6,6′‐(OH)2bpy](H2O)}[OTf]2 (Cp*=η5‐pentamethylcyclopentadienyl, bpy=2,2′‐bipyridine) was found to be a general and highly efficient catalyst for the N‐alkylation of the poor nucleophilic sulfonamides with alcohols as alkylating agents in water. The presence of OH units in the bpy ligand is crucially important for the catalytic activity of the iridium complex. Mechanistic investigations revealed that the catalytically active species is a ligand‐metal bifunctional iridium complex bearing an N,N′‐chelated 2,2′‐bipyridinated ligand and an aqua ligand. Notably, the present catalytic system and the proposed mechanism provide a new horizon and scope for the development of “hydrogen autotransfer (or hydrogen‐borrowing) processes”.magnified image

Vibrational spectroscopy of the borate mineral tunellite SrB6O9(OH)2·3(H2O) – Implications for the molecular structure

Tunellite is a strontium borate mineral with formula: SrB6O9(OH)2·3(H2O) and occurs as colorless crystals in the monoclinic pyramidal crystal system. An intense Raman band at 994cm−1 was assigned to the BO stretching vibration of the B2O3 units. Raman bands at 1043, 1063, 1082 and 1113cm−1 are attributed to the in-plane bending vibrations of trigonal boron. Sharp Raman bands observed at 464, 480, 523, 568 and 639cm−1 are simply defined as trigonal and tetrahedral borate bending modes. The Raman spectrum clearly shows intense Raman bands at 3567 and 3614cm−1, attributed to OH units. The molecular structure of a natural tunellite has been assessed by using vibrational spectroscopy.

A vibrational spectroscopic study of the silicate mineral ardennite-(As)

We have used a combination of scanning electron microscopy with EDX and vibrational spectroscopy to study the mineral ardennite-(As). The mineral ardennite-(As) of accepted formula Mn42+(Al,Mg)6(Si3O10)(SiO4)2(AsO4,VO4)(OH)6 is a silicate mineral which may contain arsenate and/or vanadates anions. Because of the oxyanions present, the mineral lends itself to analysis by Raman and infrared spectroscopy. Qualitative chemical analysis shows a homogeneous phase, composed by Si, Mn, Al and As. Ca and V were also observed in partial substitution for Mn and As. Raman bands at 1197, 1225, 1287 and 1394cm−1 are assigned to SiO stretching vibrations. The strong Raman bands at 779 and 877cm−1 are assigned to the AsO43- antisymmetric and symmetric stretching vibrations.The Raman band at 352cm−1 is assigned to the ν2 symmetric bending vibration. The series of Raman bands between 414 and 471cm−1are assigned to the ν4 out of plane bending modes of the AsO43- units. Intense Raman bands observed at 301 and 314cm−1 are attributed to the MnO stretching and bending vibrations. Raman bands at 3041, 3149, 3211 and 3298cm−1 are attributed to the stretching vibrations of OH units. There is vibrational spectroscopic evidence for the presence of water adsorbed on the ardennite-(As) surfaces.

Infrared and Raman spectroscopic characterization of the silicate mineral olmiite CaMn2+[SiO3(OH)](OH) – implications for the molecular structure

We have studied the mineral olmiite CaMn[SiO3(OH)](OH) which forms a series with its calcium analogue poldervaartite CaCa[SiO3(OH)](OH) using a range of techniques including scanning electron microscopy, thermogravimetric analysis, Raman and infrared spectroscopy. Chemical analysis shows the mineral is pure and contains only calcium and manganese in the formula. Thermogravimetric analysis proves the mineral decomposes at 502°C with a mass loss of 8.8% compared with the theoretical mass loss of 8.737%. A strong Raman band at 853cm−1 is assigned to the SiO stretching vibration of the SiO3(OH) units. Two Raman bands at 914 and 953cm−1 are attributed to the antisymmetric vibrations. Two intense Raman bands observed at 3511 and 3550cm−1 are assigned to the OH stretching vibration of the SiO3(OH) units. The observation of multiple OH bands supports the concept of the non-equivalence of the OH units. Vibrational spectroscopy enables a detailed assessment of the molecular structure of olmiite.

Infrared and Raman spectroscopic characterization of the carbonate mineral huanghoite – And in comparison with selected rare earth carbonates

Raman spectroscopy complimented with infrared spectroscopy has been used to study the rare earth based mineral huanghoite with possible formula given as BaCe(CO3)2F and compared with the Raman spectra of a series of selected natural halogenated carbonates from different origins including bastnasite, parisite and northupite. The Raman spectrum of huanghoite displays three bands are at 1072, 1084 and 1091cm−1 attributed to the CO32- symmetric stretching vibration. The observation of three symmetric stretching vibrations is very unusual. The position of CO32- symmetric stretching vibration varies with mineral composition. Infrared spectroscopy of huanghoite show bands at 1319, 1382, 1422 and 1470cm−1. No Raman bands of huanghoite were observed in these positions. Raman spectra of bastnasite, parisite and northupite show a single band at 1433, 1420 and 1554cm−1 assigned to the ν3 (CO3)2− antisymmetric stretching mode. The observation of additional Raman bands for the ν3 modes for some halogenated carbonates is significant in that it shows distortion of the carbonate anion in the mineral structure. Four Raman bands for huanghoite are observed at 687, 704, 718 and 730cm−1and assigned to the (CO3)2− ν2 bending modes. Raman bands are observed for huanghoite at around 627cm−1 and are assigned to the (CO3)2− ν4 bending modes. Raman bands are observed for the carbonate ν4 in phase bending modes at 722cm−1 for bastnasite, 736 and 684cm−1 for parisite, 714cm−1 for northupite. Raman bands for huanghoite observed at 3259, 3484 and 3589cm−1 are attributed to water stretching bands. Multiple bands are observed in the OH stretching region for bastnasite and parisite indicating the presence of water and OH units in their mineral structure. Vibrational spectroscopy enables new information on the structure of huanghoite to be assessed.

A fast organic template-free, ZSM-11 seed-assisted synthesis of ZSM-5 with good performance in methanol-to-olefin

This work demonstrated a novel and efficient route for preparing ZSM-5 zeolite by adding ZSM-11 seeds in a template-free system. Compared to conventional ZSM-5-seeded synthesis using crystallization time of 36h, ZSM-11 seeds drove the crystallization of ZSM-5 in much shorter time (12–16h). Particularly, as used hierarchical ZSM-11 seeds with intergrowth morphology, numerous small ZSM-5 crystals with size of 1–2μm could be obtained in a very short period (12h). Both the seed and product zeolites were characterized by XRD, XRF, 27Al MAS NMR, SEM, FTIR and N2 adsorption–desorption analysis. It was found that the existence of terminal Si–OH units on the surface of ZSM-11 seed particles was principally responsible for the fast crystallization of target ZSM-5 zeolites. Moreover, the external surface area provided by the seeds played a vital role in accelerating the nucleation rate by offering specific sites for the formation of nuclei. When applied in the methanol to olefins (MTO) reaction, small ZSM-5 crystals obtained in the hierarchical ZSM-11-seeded system exhibited both a high selectivity to C2=–C4= olefins and a low deactivation rate. In general, this green synthesis route gives enlightenment for designing the synthesis of zeolites with good performance by using seed crystals with special properties.

A Vibrational Spectroscopic Study of the So-Called Healing Mineral Papagoite CaCuAlSi2O6(OH)3

ABSTRACT Papagoite is a silicate mineral named after an American Indian tribe and was used as a healing mineral. Papagoite CaCuAlSi2O6(OH)3 is a hydroxy mixed anion compound with both silicate and hydroxyl anions in the formula. The structural characterization of the mineral papagoite remains incomplete. Papagoite is a four-membered ring silicate with Cu2+ in square planar coordination. The intense sharp Raman band at 1053 cm−1 is assigned to the ν1 (A 1g) symmetric stretching vibration of the SiO4 units. The splitting of the ν3 vibrational mode offers support to the concept that the SiO4 tetrahedron in papagoite is strongly distorted. A very intense Raman band observed at 630 cm−1 with a shoulder at 644 cm−1 is assigned to the ν4 vibrational modes. Intense Raman bands at 419 and 460 cm−1 are attributed to the ν2 bending modes. Intense Raman bands at 3545 and 3573 cm−1 are assigned to the stretching vibrations of the OH units. Low-intensity Raman bands at 3368 and 3453 cm−1 are assigned to water stretching modes. It is suggested that the formula of papagoite is more likely to be CaCuAlSi2O6(OH)3 · xH2O. Hence, vibrational spectroscopy has been used to characterize the molecular structure of papagoite.

Thermal analysis and vibrational spectroscopic characterization of the boro silicate mineral datolite – CaBSiO4(OH)

The objective of this work is to determine the thermal stability and vibrational spectra of datolite CaBSiO4(OH) and relate these properties to the structure of the mineral. The thermal analysis of datolite shows a mass loss of 5.83% over a 700–775°C temperature range. This mass loss corresponds to 1 water (H2O) molecules pfu. A quantitative chemical analysis using electron probe was undertaken. The Raman spectrum of datolite is characterized by bands at 917 and 1077cm−1 assigned to the symmetric stretching modes of BO and SiO tetrahedra. A very intense Raman band is observed at 3498cm−1 assigned to the stretching vibration of the OH units in the structure of datolite. BOH out-of-plane vibrations are characterized by the infrared band at 782cm−1. The vibrational spectra are based upon the structure of datolite based on sheets of four- and eight-membered rings of alternating SiO4 and BO3(OH) tetrahedra with the sheets bonded together by calcium atoms.

Vibrational spectroscopic characterization of the phosphate mineral kulanite Ba(Fe2+,Mn2+,Mg)2(Al,Fe3+)2(PO4)3(OH)3

The mineral kulanite BaFe2Al2(PO4)3(OH)3, a barium iron aluminum phosphate, has been studied by using a combination of electron microscopy and vibrational spectroscopy. Scanning electron microscopy with EDX shows the mineral is homogenous with no other phases present. The Raman spectrum is dominated by an intense band at 1022cm−1 assigned to the PO43-ν1 symmetric stretching mode. Low intensity Raman bands at 1076, 1110, 1146, 1182cm−1 are attributed to the PO43-ν3 antisymmetric stretching vibrations. The infrared spectrum shows a complex spectral profile with overlapping bands. Multiple phosphate bending vibrations supports the concept of a reduction in symmetry of the phosphate anion. Raman spectrum at 3211, 3513 and 3533cm−1 are assigned to the stretching vibrations of the OH units. Vibrational spectroscopy enables aspects on the molecular structure of kulanite to be assessed.

Vibrational spectroscopy of the phosphate mineral kovdorskite – Mg2PO4(OH)⋅3H2O

The mineral kovdorskite Mg2PO4(OH)⋅3H2O was studied by electron microscopy, thermal analysis and vibrational spectroscopy. A comparison of the vibrational spectroscopy of kovdorskite is made with other magnesium bearing phosphate minerals and compounds. Electron probe analysis proves the mineral is very pure. The Raman spectrum is characterized by a band at 965cm−1 attributed to the PO43- ν1 symmetric stretching mode. Raman bands at 1057 and 1089cm−1 are attributed to the PO43- ν3 antisymmetric stretching modes. Raman bands at 412, 454 and 485cm−1 are assigned to the PO43- ν2 bending modes. Raman bands at 536, 546 and 574cm−1 are assigned to the PO43- ν4 bending modes. The Raman spectrum in the OH stretching region is dominated by a very sharp intense band at 3681cm−1 assigned to the stretching vibration of OH units. Infrared bands observed at 2762, 2977, 3204, 3275 and 3394cm−1 are attributed to water stretching bands. Vibrational spectroscopy shows that no carbonate bands are observed in the spectra; thus confirming the formula of the mineral as Mg2PO4(OH)⋅3H2O.

Characterization of the sulphate mineral amarantite – [formula omitted] using infrared, Raman spectroscopy and thermogravimetry

The mineral amarantite Fe23+(SO4)O·7H2O has been studied using a combination of techniques including thermogravimetry, electron probe analyses and vibrational spectroscopy. Thermal analysis shows decomposition steps at 77.63, 192.2, 550 and 641.4°C. The Raman spectrum of amarantite is dominated by an intense band at 1017cm−1 assigned to the SO42-ν1 symmetric stretching mode. Raman bands at 1039, 1054, 1098, 1131, 1195 and 1233cm−1 are attributed to the SO42-ν3 antisymmetric stretching modes. Very intense Raman band is observed at 409cm−1 with shoulder bands at 399, 451 and 491cm−1 are assigned to the ν2 bending modes. A series of low intensity Raman bands are found at 543, 602, 622 and 650cm−1 are assigned to the ν4 bending modes. A very sharp Raman band at 3529cm−1 is assigned to the stretching vibration of OH units. A series of Raman bands observed at 3025, 3089, 3227, 3340, 3401 and 3480cm−1 are assigned to water bands. Vibrational spectroscopy enables aspects of the molecular structure of the mineral amarantite to be ascertained.

Vibrational spectroscopic characterization of the phosphate mineral phosphophyllite – Zn2Fe(PO4)2·4H2O, from Hagendorf Süd, Germany and in comparison with other zinc phosphates

This research was undertaken on phosphophyllite sample from the Hagendorf Süd pegmatite, Bavaria, Germany. Chemical analysis was carried out by Scanning Electron Microscope in the EDS mode and indicates a zinc and iron phosphate with partial substitution of manganese, which partially replaced iron. The calculated chemical formula of the studied sample was determined to be: Zn2(Fe0.65, Mn0.35)∑1.00(PO4)2·4(H2O). The intense Raman peak at 995cm−1 is assigned to the ν1PO43- symmetric stretching mode and the two Raman bands at 1073 and 1135cm−1 to the ν3PO43- antisymmetric stretching modes. The ν4PO43- bending modes are observed at 505, 571, 592 and 653cm−1 and the ν2PO43- bending mode at 415cm−1. The sharp Raman band at 3567cm−1 attributed to the stretching vibration of OH units brings into question the actual formula of phosphophyllite. Vibrational spectroscopy enables an assessment of the molecular structure of phosphophyllite to be assessed.

Vibrational spectroscopy of the phosphate mineral lazulite – (Mg, Fe)Al2(PO4)2·(OH)2 found in the Minas Gerais, Brazil

This research was done on lazulite samples from the Gentil mine, a lithium bearing pegmatite located in the municipality of Mendes Pimentel, Minas Gerais, Brazil. Chemical analysis was carried out by electron microprobe analysis and indicated a magnesium rich phase with partial substitution of iron. Traces of Ca and Mn, (which partially replaced Mg) were found. The calculated chemical formula of the studied sample is: (Mg0.88, Fe0.11)Al1.87(PO4)2.08(OH)2.02. The Raman spectrum of lazulite is dominated by an intense sharp band at 1060cm−1 assigned to PO stretching vibrations of of tetrahedral [PO4] clusters presents into the HPO42- units. Two Raman bands at 1102 and 1137cm−1 are attributed to both the HOP and PO antisymmetric stretching vibrations. The two infrared bands at 997 and 1007cm−1 are attributed to the ν1PO43- symmetric stretching modes. The intense bands at 1035, 1054, 1081, 1118 and 1154cm−1 are assigned to the ν3PO43- antisymmetric stretching modes from both the HOP and tetrahedral [PO4] clusters. A set of Raman bands at 605, 613, 633 and 648cm−1 are assigned to the ν4 out of plane bending modes of the PO4, HPO4 and H2PO4 units. Raman bands observed at 414, 425, 460, and 479cm−1 are attributed to the ν2 tetrahedral PO4 clusters, HPO4 and H2PO4 bending modes. The intense Raman band at 3402 and the infrared band at 3403cm−1 are assigned to the stretching vibration of the OH units. A combination of Raman and infrared spectroscopy enabled aspects of the molecular structure of the mineral lazulite to be understood.

Vibrational spectroscopic study of the mineral penkvilksite Na 2TiSi 4O 11·2H 2O – a mineral used for the uptake of radionuclides

We have used vibrational spectroscopy to study the formula and molecular structure of the mineral penkvilksite Na 2TiSi 4O 11·2H 2O. Penkvilksite is a mineral which may be used in the uptake of radioactive elements. Both Raman and infrared spectroscopies identify a band at ∼3638 cm−1 attributed to an OH-stretching vibration of hydroxyl units. The inference is that OH units are involved in the structure of penkvilksite. The formula may be well written as Na 2TiSi 4O 10(OH)2·H 2O. The mineral is characterised by a very intense Raman band at 1085 cm−1 and a broad infrared band at 1080 cm−1 assigned to SiO-stretching vibrations. Raman bands at 620, 667 and 711 cm−1 are attributed to SiO and TiO chain bonds. Water-stretching vibrations are observed as Raman bands at 3197, 3265, 3425 and 3565 cm−1. Vibrational spectroscopy enables aspects of the molecular structure of the mineral penkvilksite to be ascertained. Penkvilksite is a mineral which can incorporate actinides and lanthanides from radioactive waste.