Rami Suleiman

Anticorrosion/antifouling properties of bacterial spore-loaded sol-gel type coating for mild steel in saline marine condition: a case of thermophilic strain of Bacillus licheniformis

This work reports the performance of a sol–gel type coating encapsulated with biofilm of inoculums of protective thermophilic strain of Bacillus licheniformis endospores isolated from the Gazan hot springs-Saudi Arabia for the inhibition of marine fouling and corrosion protection of S36-grade mild steel in 3.5 wt% NaCl medium. In order to improve its anticorrosion properties, the hybrid sol–gel coating is further doped with zinc molybdate (MOLY) and zinc aluminum polyphosphate (ZAPP) pigments. Marine fouling study was conducted at the Arabia Gulf water of Half Moon Bay, Al-Khobar, Saudi Arabia for 10 weeks on the coated samples with and without the bacterial endospores. The assessment of fouling results reveals that the bacterial endospores possess antifouling potentials since it performed better compared to its abiotic counterpart within the immersion period of study due to their foul-releasing effect. Improved corrosion and fouling resistant in the presence of the bacterial endospores could be attributed to their multi-layered hydrophobic and antibiotic coating surface after bacterial encapsulation. Spores accumulation in the sol–gel coating altered the surface wetness thereby preventing the diffusion of corrosion molecules and ions through the bulk of the coating to the metal surface; this is evident in the trend of electrochemical coating resistance and capacitance. Confocal laser scanning fluorescence and scanning electron microscopies were employed to probe bacterial viability and surface micro-cracks inherent in the coating, respectively. This is the first report of axenic thermophilic strain of Bacillus licheniformis isolated from the Arabian Gulf with inhibiting potentials against corrosion and fouling of industrial steel.

Novel hybrid epoxy silicone materials as efficient anticorrosive coatings for mild steel

Novel hybrid-sol–gel materials (C1–C5) based on silica–epoxy composite resins were successfully prepared by coupling different aminosilanes with DER736 epoxy resin, followed by an in situ sol–gel process, and finally introducing the urethane moieties to the final coatings. This research has emphasized the effect of changing the type of aminosilane on the properties of the prepared hybrid coatings. Three different aminosilanes were examined and their reaction parameters with the epoxy and the trialkoxysilanes were carefully optimized in order to avoid fast gelation and to obtain the desired properties of the hybrid coatings. The prepared organic–inorganic hybrid coatings were loaded and cured on mild steel panels and characterized for FTIR, NMR, TGA, water contact angles (WCA), nanoindentation hardness, pull-off adhesion, SEM, EIS and polarization studies. The results revealed that the coatings prepared from the trialkoxysilanes APTMS and MTMS (C4) demonstrate the best mechanical, anticorrosion and adhesion properties on mild steel substrates as compared to all other coatings in a 3.5 wt% NaCl medium. Electrochemical impedance spectroscopy (EIS) results indicated a corrosion resistance value for this coating in the range of 106 Ω cm2 after 10 days of continuous immersion in the saline medium. The SEM observations suggest that coatings produced from the other aminosilanes, APT-PDMS and APM–DMS are inhomogeneous and have some defects which have ultimately affected their barrier protection properties.

Comparison of selected inhibitor doped sol–gel coating systems for protection of mild steel

Abstract Current legislation around the use of antifouling and anticorrosion coatings has increased the need to find an environment friendly alternative to existing biocide containing pretreatments for steel structures exposed to sea water. Sol–gel technology offers a solution to fouling and corrosion inhibition since sol–gel chemistry lends itself ideally to functionalisation with a variety of components, for example, corrosion inhibitors. In this study, we have utilised the above mentioned approach in order to produce an inhibitor doped sol–gel protective coating on mild steel. The corrosion protection performance of three inhibitors, i.e. SD (Shieldex303), MOLY (Moly-White101ED-PLUS) and ZAPP (Heucophos ZAPP), added individually to a sol–gel, and applied to mild steel Q panels, were evaluated using electrochemical impedance spectroscopy. The inhibitor containing coatings were shown to protect against corrosion of mild steel; the coatings containing the inhibitors Moly and ZAPP were the most effective of the systems tested. Highlights • Sol–gel coatings are potential candidate systems for the protection of mild steel substrates. • Sol–gel chemistry allows a variety of corrosion inhibitors to be incorporated into the sol–gel coating matrix. • Evaluation of corrosion inhibition efficiency of sol–gel coatings can be assessed using electrochemical impedance spectroscopy (EIS).

Probing the corrosion inhibiting role of a thermophilic Bacillus licheniformis biofilm on steel in a saline axenic culture

The growth of some bacterial biofilms has been widely reported to have defined consequences on industrial metals, and their related metabolic activities affect the overall electrochemical process of these metals in any given medium. This work seeks to unravel the role of a thermophilic Bacillus licheniformis biofilm (an isolate from the Jazan spring of Saudi Arabia) on corrosion reduction for stainless steel (316 L grade) in a saline culture medium. Grown on the steel substrate, this bacterial biofilm and the nature of its extracellular polymeric substances have been probed chemically and electrochemically for their influences on the metal dissolution within an incubation period. Corrosion inhibition in the presence of varying concentrations (in CFU ml−1) of this bacterium in the biotic-inoculate systems is explained in terms of corrosion resistance and capacitance of the biofilm. The corrosion rate of steel is found to reduce significantly in the saline culture medium within the range of concentrations of bacterium under study compared with the sterile control. This is attributed to the adhesion of a relatively compact and dense “beneficial” biofilm as well as the secretion of corrosion inhibiting substances from the bacterial biofilm as revealed during surface analysis.

A palladium–bisoxazoline supported catalyst for selective synthesis of aryl esters and aryl amides via carbonylative coupling reactions

The catalytic synthesis of aryl esters and amides has been successfully achieved in the presence of the efficient palladium–bisoxazoline supported on Merrifields resin (Pd–BOX-M). The palladium heterogeneous catalyst was prepared and characterized using various spectroscopic techniques. A bisoxazoline ligand having a suitable functional group (BOX-OH) was first synthesized, characterized, chemically supported on Merrifields resin, and finally coordinated to palladium(II) chloride. The catalytic activity and the recycling ability of the new palladium supported catalyst have been investigated in the alkoxycarbonylation and aminocarbonylation of various aryl iodides using different alkyl and aromatic alcohols and amines as nucleophiles. The palladium heterogeneous catalyst demonstrated excellent catalytic activity and very high recycling ability in the above two carbonylation reactions. The palladium heterogeneous catalysts showed an excellent stability under carbon monoxide and under the experimental conditions.

A silica-supported palladium-bis(oxazoline) complex efficiently catalyzes the synthesis of cinnamic acid derivatives via Mizoroki–Heck coupling reactions

A palladium(II)-bis(oxazoline) complex supported on silica (Pd-BOX-Si) was prepared, characterized and applied as a catalyst in Mizoroki–Heck cross-coupling reactions. The bis(oxazoline) (BOX) ligand has a hydroxyl group that can be anchored to 4-benzyl chloride-functionalized silica gel, followed by the coordination of palladium(II) chloride. The catalytic activity and the recyclability of Pd-BOX-Si have been investigated in the production of cinnamic acid derivatives via Mizoroki–Heck coupling reactions of acrylates with aryl halides; The Pd-BOX-Si catalyst demonstrated excellent catalytic activity. Characterization of the recycled Pd-BOX-Si catalyst revealed its good stability under the reaction conditions employed.

New palladium-bis(oxazoline)-phosphine complexes: synthesis, characterization and catalytic application in alkoxycarbonylation of alkynes

Abstract New cationic palladium-bis(oxazoline)-phosphine (Pd-BOX-PR3) complexes (Pd-BOX-B and Pd-BOX-C) have been synthesized and characterized using 1H, 13C and 31P NMR, FTIR spectroscopy, and electrospray ionization mass spectrometry (ESI-MS). The new complexes were used as catalysts in the alkoxycarbonylation of alkynes with various alcohols as nucleophiles. The carbonylation has produced the gem-α,β-unsaturated ester isomer (3) in high regioselectivity and excellent yields. The catalyst systems have been optimized by screening the type of palladium complexes and also by varying the reaction parameters including the reaction time, solvent, and temperature. A mechanism of the catalytic cycle based on a N-protonated palladium bis(oxazoline) phosphine active species was proposed for the alkoxycarbonylation reaction.

Effect of functionalized multiwalled carbon nanotubes on weather degradation and corrosion of waterborne polyurethane coatings

A series of waterborne polyurethane/functionalized multiwalled carbon nanotube (WBPU/f-MWCNT) nanocomposite dispersions was prepared using three defined concentrations of 0.5, 1.0 and 2.0 wt% carboxyl functionalized multiwalled carbon nanotubes (f-MWCNTs). All dispersions were coated on mild steel and exposed under natural weather condition for a maximum of 365 days. Both exposed and unexposed coatings were characterized by potentiodynamic polarization (PDP) and X-ray photoelectron spectroscopy (XPS) analyses. The pristine WBPU coating showed slight degradation and corrosion protection. Inclusion of a higher content of f-MWCNTs significantly improved both the degradation and corrosion protection efficiencies of the coatings. Maximal degradation and corrosion protection was observed when 2.0 wt% f-MWCNT was mixed with WBPU for all of the coatings.

Comparative studies on the corrosion inhibition efficacy of ethanolic extracts of date palm leaves and seeds on carbon steel corrosion in 15% HCl solution

Abstract The work reports on the study carried out to comparatively assess the corrosion inhibition efficacy of crude ethanolic extracts of date palm leaves and seeds on X60 carbon steel corrosion in 15% HCl solution at 25–60 °C. The corrosion inhibition studies was carried out using weight loss and electrochemical (potentiodynamic polarization and linear polarization resistance) techniques. Preliminary phytochemical screening was performed in order to determine the phytoconstituents present in the crude extracts. The influence of extractive solvents on the corrosion inhibition performance of the extracts was also investigated. It is found that the crude extracts of both date palm leaves and seeds contain saponins, flavonoids, cardiac glycosides and reducing sugars. Tannins is only present in the leaves and absent in the seeds while anthraquinones is absent in both extracts. The crude ethanolic extracts inhibited the corrosion of X60 steel in the aggressive 15% HCl solution with the leaves extract showing superior performance. Inhibition efficiency increased with increase in concentration of the extracts and temperature. Potentiodynamic polarization results reveal that the extracts function as mixed type inhibitors. Corrosion inhibition occurs by virtue of adsorption of components of the extract on the steel surface and was found to follow Langmuir adsorption isotherm model. On the influence of the extractive solvents on the corrosion inhibition performance, the order of inhibition efficiency at 60 °C follows the trend DPLAE (73.6%) > DPLEE (62.5%) > DPSAE (59.9%) > DPSEE (55.9%) with the optimum extract concentration (2000 ppm) studied.

Alkoxycarbonylation of α,β-unsaturated amides catalyzed by palladium(II) complexes: a DFT study of the mechanism

The reaction mechanisms of the palladium-catalyzed alkoxycarbonylation of α,β-unsaturated amides are studied by means of density functional theory (DFT) at the B3LYP/def2-TZVP//B3LYP/def2-SVP level of theory including solvent and dispersion corrections. Two possible pathways, hydride and alkoxy, are examined and their corresponding intermediates and transition structures are calculated for the alpha and beta products. The active catalytic intermediate for the first pathway is the [Pd(II)(PPh3)2(H)Cl] hydride complex, and the second considers the [Pd(II)(PPh3)2(OMe)Cl] alkoxy complex as the active species. The calculations support the palladium-catalyzed alkoxycarbonylation of α,β-unsaturated amides by a three-step reaction mechanism based on palladium-alkoxy precursor, namely, the insertion of CO into the Pd–OMe bond, the insertion of the CC amide bond into the Pd–C bond and the formation of the product, and the regeneration of the catalyst through a metathesis mechanism.