A restatement of the natural science evidence base concerning grassland management, grazing livestock and soil carbon storage.

Approximately a third of all annual greenhouse gas emissions globally are directly or indirectly associated with the food system, and over a half of these are linked to livestock production. In temperate oceanic regions, such as the UK, most meat and dairy is produced in extensive systems based on pasture. There is much interest in the extent to which such grassland may be able to sequester and store more carbon to partially or completely mitigate other greenhouse gas emissions in the system. However, answering this question is difficult due to context-specificity and a complex and sometimes inconsistent evidence base. This paper describes a project that set out to summarize the natural science evidence base relevant to grassland management, grazing livestock and soil carbon storage potential in as policy-neutral terms as possible. It is based on expert appraisal of a systematically assembled evidence base, followed by a wide stakeholders engagement. A series of evidence statements (in the appendix of this paper) are listed and categorized according to the nature of the underlying information, and an annotated bibliography is provided in the electronic supplementary material.

A restatement of the natural science evidence base regarding the source, spread and control of Campylobacter species causing human disease.

Food poisoning caused by Campylobacter (campylobacteriosis) is the most prevalent bacterial disease associated with the consumption of poultry, beef, lamb and pork meat and unpasteurized dairy products. A variety of livestock industry, food chain and public health interventions have been implemented or proposed to reduce disease prevalence, some of which entail costs for producers and retailers. This paper describes a project that set out to summarize the natural science evidence base relevant to campylobacteriosis control in as policy-neutral terms as possible. A series of evidence statements are listed and categorized according to the nature of the underlying information. The evidence summary forms the appendix to this paper and an annotated bibliography is provided in the electronic supplementary material.

Multimetallic Permethylpentalene Hydride Complexes.

The synthesis and characterization of group 4 permethylpentalene (Pn* = C8Me6) hydride complexes are explored; in all cases, multimetallic hydride clusters were obtained. Group 4 lithium metal hydride clusters were obtained when reacting the metal dihalides with hydride transfer reagents such as LiAlH4, and these species featured an unusual hexagonal bipyramidal structural motif. Only the zirconium analogue was found to undergo hydride exchange in the presence of deuterium. In contrast, a trimetallic titanium hydride cluster was isolated on reaction of the titanium dialkyl with hydrogen. This diamagnetic, mixed valence species was characterized in the solid state, as well as by solution electron paramagnetic resonance and nuclear magnetic resonance spectroscopy. The structure was further probed and corroborated by density functional theory calculations, which illustrated the formation of a metal-cluster bonding orbital responsible for the diamagnetism of the complex. These permethylpentalene hydride complexes have divergent structural motifs and reactivity in comparison with related classical cyclopentadienyl analogues.

Controlling the Surface Hydroxyl Concentration by Thermal Treatment of Layered Double Hydroxides.

Layered double hydroxides (LDHs) are important materials in the field of catalyst supports, and their surface hydroxyl functionality makes them interesting candidates for supporting well-defined single-site catalysts. Here, we report that the surface hydroxyl concentration can be controlled by thermal treatment of these materials under vacuum, leading to hydroxyl numbers (αOH) similar to those of dehydroxylated silica, alumina, and magnesium hydroxide. Thermal treatment of [Mg0.74Al0.26(OH)2](SO4)0.1(CO3)0.03·0.62(H2O)·0.04(acetone) prepared by the aqueous miscible organic solvent treatment method (Mg2.84Al-SO4-A AMO-LDH) is shown to yield a mixed metal oxide above 300 °C by a combination of thermogravimetric analysis, powder X-ray diffraction (PXRD), BET surface area analysis, and FTIR spectroscopy. PXRD shows the disappearance of the characteristic LDH 00l peaks at 300 °C indicative of decomposition to the layered structure, coupled with a large increase in the BET surface area (95 vs 158 m2 g-1 from treatment at 275 and 300 °C, respectively). Titration of the surface hydroxyls with Mg(CH2Ph)2(THF)2 indicates that the hydroxyl number is independent of surface area for a given treatment temperature. Treatment at 450 °C under vacuum produces a mixed metal oxide material with a surface hydroxyl concentration (αOH) of 2.14 OH nm-2 similar to the hydroxyl number (αOH) of 1.80 OH nm-2 for a sample of SiO2 dehydroxylated at 500 °C. These materials appear to be suitable candidates for use as single-site organometallic catalyst supports.

Optimising the acid-base ratio of Mg-Al layered double oxides to enhance CO2 capture performance: the critical role of calcination conditions.

The effect of calcination conditions (ramp rate, calcination temperature and time) on the formation of Mg2Al layered double oxides (Mg2Al LDOs) as well as their CO2 capture performance, has been systematically investigated. This study explores novel insights into the intricate relationship between these calcination conditions and the resulting surface characteristics, which play a vital role in CO2 capture efficiency. Notably, it is revealed that a rapid ramp rate (100 °C min-1) significantly increases surface area and hydroxyl concentration, leading to a 69% increase in CO2 capture efficiency compared to slower ramp rate. Conversely, short calcination times (1 h) and fast ramp rates (100 °C min-1) are observed to compromise CO2 adsorption due to the presence of dehydrated LDHs. A critical acid : base ratio of 0.37, achieved from a fast ramp rate (100 °C min-1) at 400 °C for 2 h, was found as a key threshold for optimising surface properties, effectively balancing favourable hydroxyl and less favourable strong acid sites, thereby maximizing CO2 capture performance.

Trends in Structure and Ethylene Polymerization Reactivity of Transition-Metal Permethylindenyl-phenoxy (PHENI*) Complexes.

A family of ansa-permethylindenyl-phenoxy (PHENI*) transition-metal chloride complexes has been synthesized and characterized (1-7; {(η5-C9Me6)Me(R″)Si(2-R-4-R'-C6H2O)}MCl2; R,R' = Me, tBu, Cumyl (CMe2Ph); R″ = Me, nPr, Ph; M = Ti, Zr, Hf). The ancillary chloride ligands could readily be exchanged with halides, alkyls, alkoxides, aryloxides, or amides to form PHENI* complexes [L]TiX2 (8-17; X = Br, I, Me, CH2SiMe3, CH2Ph, NMe2, OEt, ODipp). The solid-state crystal structures of these PHENI* complexes indicate that one of two conformations may be preferred, parametrized by a characteristic torsion angle (TA'), in which the η5 system is either disposed away from the metal center or toward it. Compared to indenyl PHENICS complexes, the permethylindenyl (I*) ligand appears to favor a conformation in which the metal center is more accessible. When heterogenized on solid polymethylaluminoxane (sMAO), titanium PHENI* complexes exhibit exceptional catalytic activity toward the polymerization of ethylene. Substantially greater activities are reported than for comparable PHENICS catalysts, along with the formation of ultrahigh-molecular-weight polyethylenes (UHMWPE). Catalyst-cocatalyst ion pairing effects are observed in cationization experiments and found to be significant in homogeneous catalytic regimes; these effects are also related to the influence of the ancillary ligand leaving groups in slurry-phase polymerizations. Catalytic efficiency and polyethylene molecular weight are found to increase with pressure, and PHENI* catalysts can be categorized as being among the most active for the controlled synthesis of UHMWPE.

Fully tuneable ethylene-propylene elastomers using a supported permethylindenyl-phenoxy (PHENI*) catalyst.

Using a highly active supported permethylindenyl-phenoxy (PHENI*) titanium catalyst, high molecular weight ethylene-propylene (EPM) and ethylene-propylene-diene (EPDM) elastomers are prepared using slurry-phase catalysis. Final copolymer composition was found to reflect the monomer feed ratio in a linear fashion, to access a continuum of material properties with a single catalyst. Post-polymerisation crosslinking of EPDM was also demonstrated in a model sulfur vulcanisation system.

Towards designer polyolefins: highly tuneable olefin copolymerisation using a single permethylindenyl post-metallocene catalyst.

Using a highly active permethylindenyl-phenoxy (PHENI*) titanium catalyst, high to ultra-high molecular weight ethylene-linear-α-olefin (E/LAO) copolymers are prepared in high yields under mild conditions (2 bar, 30-90 °C). Controllable, efficient, and predictable comonomer enchainment provides access to a continuum of copolymer compositions and a vast range of material properties using a single monomer-agnostic catalyst. Multivariate statistical tools are employed that combine the tuneability of this system with the analytical and predictive power of data-derived models, this enables the targeting of polyolefins with designer properties directly through predictive alteration of reaction conditions.

Synthesis, characterization, and lactide polymerization activity of group 4 metal complexes containing two bis(phenolate) ligands.

A series of group 4 metal complexes Zr-(1)(2), Zr-(2)(2), Zr-(3)(2), Zr-(4)(2), Zr-(5)(2), Hf-(1)(2), and Hf-(4)(2) containing two bridged bis(phenolate) ligands of the (OSSO)-type were prepared by the reaction of the corresponding bis(phenol) and group 4 metal precursor MX(4) (X = O(i)Pr, CH(2)Ph) and isolated as robust, colorless crystals. NMR spectra indicate D(2) symmetry, in agreement with the solid state structure determined by single crystal X-ray diffraction study of the complexes Zr-(1)(2), Hf-(1)(2), Zr-(3)(2), Zr-(4)(2), and Zr-(5)(2). The complexes with the 1,4-dithiabutanediyl bridged ligands exhibit a highly symmetric coordination around the metal center. The introduction of the rigid trans-1,2-cyclohexanediyl bridged ligands led to a distorted coordination around the metal center in Zr-(4)(2) and Zr-(5)(2) when the ortho substituent is tert-butyl and the para substituent is larger than methyl. The complexes Zr-(1)(2), Zr-(2)(2), Zr-(3)(2), Zr-(4)(2) as well as Hf-(1)(2) and Hf-(4)(2) initiated the ring-opening polymerization of meso-lactide at 100 °C to give heterotactic polylactide with pronounced heterotacticity (>70%) and varying polydispersity (1.05 < M(w)/M(n) < 1.61). As shown by kinetic studies, zirconium complex Zr-(1)(2) polymerized meso-lactide faster than the homologous hafnium complex Hf-(1)(2).

Sterically rigid bismuth pincer complexes; observation of the growing polymer chain in polar monomer polymerisation.

A family of pyridine dipyrrolide bismuth complexes (Mes,PhL)MX (1-6) (M = Bi, X = O-2,6-Me-C6H3 = OXyl (1); M = Sb, X = OXyl (2); M = Bi, X = O-2,6-iPr-C6H3 = ODipp (3), O-2,6-tBu-C6H3 = OArtBu (4), OtBu (5) and OCMe2Et = OAm (6), N(SiMe3)2 = N'' (7) and CH2Ph (8)) have been prepared and investigated as initiators for the ring-opening polymerisation of lactide monomers. Bismuth lactate complexes (Mes,PhL)Bi{OC(H)(Me)C(O)OR} were prepared as models for the propagating species (R = tBu (9), Me (10), iPr (11)). The first insertion of the lactide monomer is rate limiting and the second and subsequent insertions are more rapid (kinit ≪ kLA2 < kprop), leading to a significant induction period. The sterically demanding, rigid pincer ligand affords a well-defined coordination environment at the metal centre and allows for the enchainment of two lactide monomers to be differentiated spectroscopically ((Mes,PhL)Bi{OC(H)(Me)C(O)}4OX (12-X)), with this species also implied to be the true initiator for the regime of propagation with first order kinetics. Well-controlled first order kinetic data for the polymerisation of L-, D-, rac- and meso-lactide are observed.

Supported permethylindenyl titanium catalysts for the synthesis of disentangled ultra-high molecular weight polyethylene (disUHMWPE).

Novel permethylindenyl-phenoxide (PHENI*) ansa-metallocene titanium complexes have been synthesised and immobilised on inorganic solid supports to afford highly effective catalysts for slurry-phase ethylene polymerisation. When supported on solid polymethylaluminoxane these complexes were both extremely active (up to 3.7 × 106 gPE molTi-1 h-1 bar-1) and produced substantially disentangled polyethylene with a weight-average molecular weight (Mw) of 3.4 MDa (disUHMWPE).

Synthesis of ultra-high molecular weight poly(ethylene)-co-(1-hexene) copolymers through high-throughput catalyst screening.

A family of permethylindenyl titanium constrained geometry complexes, Me2SB(R'N,3-RI*)TiX2 ((3-R-η5-C9Me5)Me2Si(R'TiX2)), supported on solid polymethylaluminoxane (sMAO) are investigated as slurry-phase catalysts for ethylene/H2 homopolymerisation and ethylene/1-hexene copolymerisation by high-throughput catalyst screening. Me2SB( tBuN,I*)TiCl2 supported on sMAO [sMAO-Me2SB( tBuN,I*)TiCl2] is responsive to small quantities of H2 (<1.6%), maintaining high polymerisation activities (up to 4900 kgPE molTi -1 h-1 bar-1) and yielding polyethylenes with significantly decreased molecular weight (M w) (from 2700 to 41 kDa with 1.6% H2). In slurry-phase ethylene/1-hexene copolymerisation studies, a decrease in polymerisation activity and polymer molecular weights compared to ethylene homopolymerisation is observed. Compared to many solid supported system, these complexes all display high 1-hexene incorporation levels up to a maximum incorporation of 14.2 mol% for sMAO-Me2SB(iPrN,I*)TiCl2). We observe a proportionate increase in 1-hexene incorporation with concentration, highlighting the ability of these catalysts to controllably tune the amount of 1-hexene incorporated into the polymer chain to produce linear low-density polyethylene (LLDPE) materials.

Synthesis of zirconocene complexes and their use in slurry-phase polymerisation of ethylene.

A new family of zirconocene complexes of the type (3-RInd#)2ZrX2 (where Ind# = C6Me5H and R = Me, Et and Ph) have been synthesised and fully characterised. Six new crystal structures have been reported (meso-(3-EtInd#)2ZrBr2, rac-(3-EtInd#)2ZrCl2, rac-(3-EtInd#)2Zr(CH2Ph)2, meso-(3-EtInd#)2Zr(CH2Ph)2, meso-(3-MeInd#)2ZrBr2 and meso-(3-MeInd#)2Zr(CH2Ph)2). The complexes were studied for slurry-phase ethylene polymerisation when immobilised on solid polymethylaluminoxane (sMAO). Variation in the initiation group was found to have greater influence over polymerisation activity for meso-catalysts than rac-catalysts, with meso-alkyl catalysts showing higher polymerisation activities than meso-halide. Below 70 °C, polymerisation activity follows the order sMAO-meso-(3-EtInd#)2Zr(CH2Ph)2, sMAO-meso-(3-EtInd#)2ZrCl2 and sMAO-meso-(3-EtInd#)2ZrBr2 (activities of 657, 561, and 452 kgPE molM -1 h-1 bar-1, respectively). sMAO-meso-(3-EtInd#)2ZrBr2 produces HDPE with the highest molecular weight, followed by sMAO-meso-(3-EtInd#)2ZrCl2 and sMAO-meso-(3-EtInd#)2Zr(CH2Ph)2 (M w of 503, 406, and 345 kg mol-1, respectively, at 50 °C). sMAO-meso-(3-MeInd#)2ZrBr2 produced HDPE with almost identical molecular weights to sMAO-meso-(3-EtInd#)2ZrCl2 (395 kg mol-1 at 50 °C).

Aged layered double hydroxide nanosheet-polyvinyl alcohol dispersions for enhanced gas barrier coating performance.

Whilst applying a coating layer to a polymer film is a routine approach to enhance the gas barrier properties of the film, it is counter-intuitive to consider that the gas barrier performance of the film would improve by ageing the coating dispersion for weeks before application. Herein, we report that the oxygen barrier performance of a 12 µm PET film coated with a dispersion of inorganic nanosheets in polyvinyl alcohol can be significantly enhanced by ageing this coating dispersion for up to 8 weeks before application. We found up to a 37-fold decrease in the oxygen transmission rate (OTR) of the PET coated film using aged dispersions of [Mg0.66Al0.33(OH)2](NO3)0.33 layered double hydroxide nanosheets (Mg2Al-LDH NS) in polyvinyl alcohol (PVA) compared to the film coated with an equivalent freshly prepared LDH/PVA dispersion. A limiting OTR value of 0.31 cc m-2 day-1 was achieved using the PET film coated with a 3 week aged LDH NS/PVA dispersion. X-ray diffraction experiments show that the degree of in plane alignment of LDH NS on the PET film surface increased significantly from 70.6 ± 0.6 to 86.7 ± 0.6 (%) (100% represents complete alignment of LDH NS platelets on the film surface) for the 4 week aged dispersion compared to the freshly prepared layer. We postulate that when the Mg2Al-LDH NS are aged in PVA the coiled PVA aggregates start to unwrap and attach onto the Mg2Al-LDH NS through hydrogen bonding and eventually form a hydrogen bonded ordered network that facilitates the alignment of nanosheet dispersions during the coating process. Our results suggest that the ageing of inorganic nanosheet dispersions in PVA or other potential hydrogen bonding adhesive systems could be a general approach to improve the alignment of the nanosheets on the polymer film surface once applied and thus improve their performance characteristics for barrier coating applications.

Ni2Mn-layered double oxide electrodes in organic electrolyte based supercapacitors.

The development of future mobility (e.g. electric vehicles) requires supercapacitors with high voltage and high energy density. Conventional active carbon-based supercapacitors have almost reached their limit of energy density which is still far below the desired performance. Advanced materials, particularly metal hydroxides/oxides with tailored structure are promising supercapacitor electrodes to push the limit of energy density. To date, research has largely focused on evaluation of these materials in aqueous electrolyte, while this may enable high specific capacitance, it results in low working voltage window and poor cycle stability. Herein, we report the development of Ni2Mn-layered double oxides (Ni2Mn-LDOs) as mixed metal oxide-based supercapacitor electrodes for use in an organic electrolyte. Ni2Mn-LDO obtained by calcination of [Ni0.66Mn0.33(OH)2](CO3)0.175·nH2O at 400 °C produced the best performing Ni2Mn-LDOs with high working voltage of 2.5 V and a specific capacitance of 44 F g-1 (at 1 A g-1). We believe the performance of the Ni2Mn-LDOs is related to its unique porous structure, high surface area and the homogeneous mixed metal oxide network. Ni2Mn-LDO outperforms both the single metal oxides (NiO, MnO2) and the equivalent physical mixture of the two oxides. We propose this performance boost arises from synergy between NiO and MnO x due to a more effective homogeneous network of NiO/MnO x domains in the Ni2Mn-LDO. This work clearly shows the advantage of an LDO over the single component metal oxides as well as the physical mixture of mixed metal oxides and highlights the possibilities of development of further mixed metal oxides-based supercapacitors in organic electrolyte using LDH precursors.

CO2 activation by permethylpentalene amido zirconium complexes.

We report the synthesis and characterisation of new permethylpentalene zirconium bis(amido) and permethylpentalene zirconium cyclopentadienyl mono(amido) complexes, and their reactivity with carbon dioxide.

Ring-opening polymerisation of l- and rac-lactide using group 4 permethylpentalene aryloxides and alkoxides.

A new family of group 4 permethylpentalene (C8Me62-; Pn*) aryloxide and alkoxide complexes have been synthesised and fully characterised by multinuclear NMR spectroscopy and single-crystal X-ray diffraction; (η8-C8Me6)Zr(OR)2 (R = tBu (1), 2,6-Me-C6H3 (2), 2,6-iPr-C6H3 (3) and 4-OMe-C6H4 (4)), (η8-C8Me6)Zr (OR) (R = 2,6-tBu-C6H3 (5) and 2,6-tBu-4-Me-C6H2 (6)), (η8-C8Me6)ZrCp(OR) (R = tBu (7), 2,6-Me-C6H3 (8) and 2,6-iPr-C6H3 (9)), (η8-C8Me6)TiCp(O-2,6-Me-C6H3) (10) and (η8-C8Me6)ZrCpMe(OR) (R = 2,6-Me-C6H3 (11), 2,6-iPr-C6H3 (12) and 2,4-tBu-C6H3 (13)). 2, 3, 6, 7, 9, 10 and 12 were studied as initiators for the ring-opening polymerisation (ROP) of l-lactide, and 2, 3, 6, 7 and 10 were studied as initiators for the ROP of rac-lactide. 3 was found to be the most active initiator for the ROP of l-lactide (kobs = 0.35 h-1) and 2 for the ROP of rac-lactide (kobs = 0.21 h-1). These initiators produced isotactic PLA for the ROP of l-lactide and moderately heterotactic enriched (maximum Pr of 0.69) or atactic PLA for the ROP of rac-lactide with polymer chains consisting of polylactic acid repeat units with -OR and -OH end groups.

Chiral indium alkoxide complexes as initiators for the stereoselective ring-opening polymerization of rac-lactide.

The indium complex InL(2)N'' has been prepared from the reaction of 2 equiv of ((t)Bu)(2)P(O)CH(2)CH((t)Bu)OH (HL) with InN''(3) (N'' = N(SiMe(3))(2)). This complex reacts with a further equivalent of 2,6-di-tert-butylphenol or HL to afford the adducts InL(2)(OAr) and InL(3), respectively. Confirmation that the anion L(-) exhibits "ligand self-recognition" in the formation of predominantly homochiral complexes RR-InL(2)N'' and SS-InL(2)N'' is obtained from (1)H and (31)P NMR spectroscopic data. However, the self-recognition is less effective at the indium cation, and mixtures of InL(3) complexes with different configurations are observed. Single-crystal X-ray diffraction data confirm the five-coordinate, distorted bipyramidal In center in InL(2)N'' and InL(2)(OAr) as anticipated. Selected crystals of InL(3) show two of the possible configurations: one is the fac-RRR-InL(3) complex, analogous to the lanthanide complexes LnL(3) reported previously (Ln = Y, Eu, Er, Yb); another is the alternative, homochiral mer form RRR'-InL(3). All three complexes are efficient single-component initiators for the ring-opening polymerization of rac-lactide over a wide range of temperatures and monomer-to-initiator ratios, exhibiting reasonable control over the synthesis of isotactic polylactide. Despite its poorly defined structure, InL(3) is the fastest initiator among the three complexes for the polymerization of rac-lactide, and shows the best tacticity control. The polylactide samples have high molecular weights M(n,exp) (between 44 000 and 270 000 g/mol at completion) and narrow polydispersities (as low as 1.25 at completion).

Surface modification of aqueous miscible organic layered double hydroxides (AMO-LDHs).

Silane modification of layered double hydroxides (LDHs) plays an important role in controlling the surface hydrophobicity and improving the compatibility of LDHs dispersed in non-polar materials. However, the surface modification of conventional LDHs in hydrous conditions typically results in aggregated particle morphologies, low surface areas and accessible pore volumes. In this study, well dispersed and high surface area silane grafted AMO-Zn2MgAl-CO3 LDH were prepared using the silane coupling agents (triethoxyvinylsilane (TEVS), triethoxyoctylsilane (TEOS) and (3-glycidyloxypropyl)trimethoxysilane (TMGPS)) in anhydrous acetone. Solution 1H NMR spectroscopy was initially used to study the rate and extent of silane reactivity with AMO-Zn2MgAl-CO3 LDH. Powder XRD, TEM, N2 BET specific surface area and total pore volume measurements showed that the structure and morphology of silane-treated AMO-Zn2MgAl-CO3 LDHs remained largely unchanged. Solid state 13C CP-MAS, 27Al DP-MAS and 29Si CP-MAS NMR spectroscopy indicates that the silanes have been successfully grafted onto the surface of the LDH. In addition to maintaining their structure, morphology, high surface area and total pore volume, these surface-functionalised LDHs are now more hydrophobic, displaying a saturation water vapour uptake (<4 wt%) that is ca. 60% lower than the untreated AMO-LDH.

Aspect Ratio Control of Layered Double Hydroxide Nanosheets and Their Application for High Oxygen Barrier Coating in Flexible Food Packaging.

We report a method to rationally control the aspect ratio of layered double hydroxide for use as a barrier coating for food packaging films. The reconstruction of a Mg2Al-layered double oxide (LDO) in concentrated aqueous glycine solutions produces dispersions of Mg2Al-LDH nanosheets. The nanosheet thickness decreases and diameter increases with increasing reconstruction time from 16 to 96 h. We observe a limiting nanosheet aspect ratio of ca. 336 ± 170. These Mg2Al-LDH nanosheets can be dispersed in PVA to give a water-based dispersion that can be used to coat flexible polymeric films. Oxygen transmission rate (OTR) of a PET film decreases when the thickness of the dried coated layer increases, an OTR of <0.005 mL·m-2·day-1 is observed for a coating with thickness of 1175 ± 101 nm.