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A polymerization methodology is reported using sulfur monochloride (S

The production of elemental sulfur from petroleum refining has created a technological opportunity to increase the valorization of elemental sulfur by the synthesis of high-performance sulfur-based plastics with improved optical, electrochemical, and mechanical properties aimed at applications in thermal imaging, energy storage, self-healable materials, and separation science. In this Perspective, we discuss efforts in the past decade that have revived this area of organosulfur and polymer chemistry to afford a new class of high-sulfur-content polymers prepared from the polymerization of liquid sulfur with unsaturated monomers, termed inverse vulcanization.

The production of elemental sulfur from petroleum refining has created a technological opportunity to increase the valorization of elemental sulfur by the creation of high-performance sulfur based plastics with improved thermomechanical properties, elasticity and flame retardancy. We report on a synthetic polymerization methodology to prepare the first example of sulfur based segmented multi-block polyurethanes (SPUs) and thermoplastic elastomers that incorporate an appreciable amount of sulfur into the final target material. This approach applied both the inverse vulcanization of S8 with olefinic alcohols and dynamic covalent polymerizations with dienes to prepare sulfur polyols and terpolyols that were used in polymerizations with aromatic diisocyanates and short chain diols. Using these methods, a new class of high molecular weight, soluble block copolymer polyurethanes were prepared as confirmed by Size Exclusion Chromatography, NMR spectroscopy, thermal analysis, and microscopic imaging. These sulfur-based polyurethanes were readily solution processed into large area free standing films where both the tensile strength and elasticity of these materials were controlled by variation of the sulfur polyol composition. SPUs with both high tensile strength (13-24 MPa) and ductility (348 % strain at break) were prepared, along with SPU thermoplastic elastomers (578 % strain at break) which are comparable values to classical thermoplastic polyurethanes (TPUs). The incorporation of sulfur into these polyurethanes enhanced flame retardancy in comparison to classical TPUs, which points to the opportunity to impart new properties to polymeric materials as a consequence of using elemental sulfur.

Small-molecule catalysts inspired by the active sites of [FeFe]-hydrogenase enzymes have long struggled to achieve fast rates of hydrogen evolution, long-term stability, water solubility, and oxygen compatibility. We profoundly improved on these deficiencies by grafting polymers from a metalloinitiator containing a [2Fe-2S] moiety to form water-soluble poly(2-dimethylamino)ethyl methacrylate metallopolymers (

We report on the fabrication of wholly polymeric one-dimensional (1-D) photonic crystals (i.e., Bragg reflectors, Bragg mirrors) via solution processing for use in the near (NIR) and the short wave (SWIR) infrared spectrum (1–2 μm) with very high reflectance (R ∼ 90–97%). Facile fabrication of these highly reflective films was enabled by direct access to solution processable, ultrahigh refractive index polymers, termed, Chalcogenide Hybrid Inorganic/Organic Polymers (CHIPs). The high refractive index (n) of CHIPs materials (n = 1.75–2.10) allowed for the production of narrow band IR Bragg reflectors with high refractive index contrast (Δn ∼ 0.5) when fabricated with low n polymers, such as cellulose acetate (n = 1.47). This is the highest refractive index contrast (Δn ∼ 0.5) demonstrated for an all-polymeric Bragg mirror which directly enabled high reflectivity from films with 22 layers or less. Facile access to modular, thin, highly reflective films from inexpensive CHIPs materials offers a new route to ...

Enhanced cathodes for Li–S batteries with sulfur-MoS2 composites demonstrated recently are capable to extend cycle lifetimes up to 1000 cycles with 0.07% capacity decay per cycle and deliver reversible capacity up to 500 mAh/g at 5C. To understand the origins of such remarkable performance, we investigated in-depth the cathode structures and their transformations during cycling at various scales down to the atomic level. We show that 3D interfacial structures involving mechanically activated defective 2H-MoS2 particulates and aggregated conducting nanocarbons play a critical role in enabling to maintain cathode integrity, electrocatalytically bind Li2Sx polysulfides, and effectively reduce charge transfer resistance.

Optical technologies in the midwave and long wave infrared spectrum (MWIR, LWIR) are important systems for high resolution thermal imaging in near, or complete darkness. While IR thermal imaging has been extensively utilized in the defense sector, application of this technology is being driven toward emerging consumer markets and transportation. In this viewpoint, we review the field of IR thermal imaging and discuss the emerging use of synthetic organic and hybrid polymers as novel IR transmissive materials for this application. In particular, we review the critical role of elemental sulfur as a novel feedstock to prepare high refractive index polymers via inverse vulcanization and discuss the fundamental chemical insights required to impart improved IR transparency into these polymeric materials.

We report on the conformal coating of thickness-tunable multilayers directly onto the sulfur (S8) cathodes by the layer-by-layer (LbL) deposition for the significant improvement in the performances of Li–S batteries even without key additives (LiNO3) in the electrolyte. Poly(ethylene oxide) (PEO)/poly(acrylic acid) (PAA) multilayers on a single poly(allylamine hydrochloride) (PAH)/PAA priming bilayer, deposited on the S8 cathodes, effectively protected from the polysulfide leakage, while providing a Li+ ion diffusion channel. As a result, PAH/PAA/(PEO/PAA)3 multilayer-coated cathodes exhibited the highest capacity retention (806 mAh g–1) after 100 cycles at 0.5 C, as well as the high C-rate capability up to 2.0 C. Furthermore, the multilayer coating effectively mitigated the polysulfide shuttle effect in the absent of LiNO3 additives in the electrolyte.

We show here how differences in surface composition for monolayer (ML)-tethered pyridine (Py)-treated CdSe quantum dots (QDs) affect band edge energetics, as a function of QD diameter. We compare U...

Elemental sulfur (S8) is an inexpensive chemical feedstock for polymeric materials but has the disadvantages of poor solubility in organic media and inferior physical properties in the elemental form. We report on the preparation of organosulfur chalcogenide hybrid inorganic/organic polymer (CHIPs) based on bifunctional norbornene comonomers using dynamic covalent polymerization (DCP). A poly(sulfur-random-styrene) (p(S-r-Sty)) resin was utilized to address the limited solubility/ miscibility of norbornene-containing comonomers in liquid sulfur. This report demonstrated the ability to expand the scope of organic comonomers to prepare organosulfur CHIPs from elemenatal sulfur using a combination of inverse vulcanization and dynamic covalent polymerization.

The development of an intriguing concept using optical polymers for photonics is reported to enable modulation of refractive index (RI) in solution cast thin films with precise spatial control. While extensive efforts in polymer science have focused on methods to prepare optically transparent polymers with high RI, the creation of photoresponsive polymer systems to spatially adjust the refractive index upon irradiation is a distinct technical challenge requiring development of materials amenable to this process. The ability to create refractive index contrast (i.e., a difference in RI between two domains) is a critical capability required in photonics for the fabrication of integrated photonics devices, such as, polymer waveguides. In this report, we detail the synthesis of optical polymers tailored to this application, termed Refractive Index Contrast (RIC) polymers, in which the RI of the material can be photopatterned where UV exposure in the presence of a photoacid generator resulted in a permanent increase of RI in the exposed regions thus creating regions of high RIC. This process creates the high RI core of waveguides in a single step and lends itself to rapid fabrication of photonic devices via direct laser writing. Waveguides made from RIC polymers were found to have propagation losses of ∼2 dB/cm at 1550 nm.

We report on a new strategy for preparing polymer–nanoparticle composite Faraday rotators for use in magnetic sensing and optical isolation. While most applications of Faraday rotators make use of inorganic garnet crystals, these are generally limited by low magneto-optical activity (low Verdet constants), high cost, and/or limited processing options. This has led to an interest in new materials with improved activity and processing characteristics. We have developed a new type of magneto-optical material based on polymer–nanoparticle composites that can be completely prepared by solution processing methods with tunable Verdet constants and device sensitivity. By exchanging native surface ligands on magneto-optically active CoFe2O4 nanocrystals with polymer compatible ligands, enhanced nanoparticle dispersion in processible polymer matrices was observed at up to 15 wt% inorganic loading. Employing a multilayer polymer film construct, functional Faraday rotator devices were prepared by simple sequential spin-coating of active nanocomposite and protective, barrier cellulose acetate layers. For these assemblies, magneto-optic activity and sensitivity are easily tuned through variation of nanoparticle feed and control of polymer film layers, respectively. These multilayered Faraday rotators show up to a 10-fold enhancement in Verdet constant compared to reference terbium gallium garnets at 1310 nm, opening new possibilities for the fabrication of “plastic garnets” as low cost alternatives to existing inorganic materials for use in the near-IR.

In this concept review, the fundamental and polymerization chemistry of inverse vulcanization for the preparation of statistical and segmented sulfur copolymers, which have been actively developed and advanced in various applications over the past decade is discussed. This concept review delves into a discussion of step-growth polymerization constructs to describe the inverse vulcanization process and discuss prepolymer approaches for the synthesis of segmented sulfur polyurethanes. Furthermore, this concept review discusses the advantages of inverse vulcanization in conjunction with dynamic covalent polymerization and post-polymerization modifications to prepare segmented block copolymers with enhanced thermomechanical and flame retardant properties of these materials.

Optical technologies in the long-wave infrared (LWIR) spectrum (7-14 μm) offer important advantages for high-resolution thermal imaging in near or complete darkness. The use of polymeric transmissive materials for IR imaging offers numerous cost and processing advantages but suffers from inferior optical properties in the LWIR spectrum. A major challenge in the design of LWIR-transparent organic materials is that nearly all organic molecules absorb in this spectral window which lies within the so-called IR-fingerprint region. We report on a new molecular-design approach to prepare high refractive index polymers with enhanced LWIR transparency. Computational methods were used to accelerate the design of novel molecules and polymers. Using this approach, we have prepared chalcogenide hybrid inorganic/organic polymers (CHIPs) with enhanced LWIR transparency and thermomechanical properties via inverse vulcanization of elemental sulfur with new organic co-monomers.

[2Fe–2S] organometallic complexes are effective electrocatalysts for the reduction of weak acids in acetonitrile to generate molecular hydrogen (H2) (hydrogen evolution reaction, HER). Inco...

Reviewed herein is the development of novel polymer-supported [2Fe-2S] catalyst systems for electrocatalytic and photocatalytic hydrogen evolution reactions. [FeFe] hydrogenases are the best known naturally occurring metalloenzymes for hydrogen generation, and small-molecule, [2Fe-2S]-containing mimetics of the active site (H-cluster) of these metalloenzymes have been synthesized for years. These small [2Fe-2S] complexes have not yet reached the same capacity as that of enzymes for hydrogen production. Recently, modern polymer chemistry has been utilized to construct an outer coordination sphere around the [2Fe-2S] clusters to provide site isolation, water solubility, and improved catalytic activity. In this review, the various macromolecular motifs and the catalytic properties of these polymer-supported [2Fe-2S] materials are surveyed. The most recent catalysts that incorporate a single [2Fe-2S] complex, termed single-site [2Fe-2S] metallopolymers, exhibit superior activity for H2 production.

Recent developments in the polymerization of elemental sulfur and the preparation of functional Chalcogenide Hybrid Inorganic/Organic Polymers (CHIPs) are reviewed. CHIPs represent a class of polymers synthesized from elemental sulfur with the incorporation of inorganic chalcogenide components (S, Se, Te) into the organic polymeric backbones. Novel CHIP materials exhibit interesting optical, electrochemical and mechanical properties that lead to applications in thermal imaging, energy storage, self-healable materials and separation science. The emphasis of this review is on the key advances in the synthetic approaches to prepare functional polymeric sulfur-rich materials, with recent developments in synthesis, characterization, and application milestones being highlighted.

Porous conjugated polymers offer enormous potential for energy storage because of the combined features of pores and extended π-conjugated structures. However, the drawbacks such as low pore volumes and insolubilities of micro- and mesoporous conjugated polymers restrict the loading of electroactive materials and thus energy storage performance. Herein, we report the synthesis of iron-doped macroporous conjugated polymers for hosting sulfur as the cathode of high-performance lithium–sulfur (Li–S) batteries. The macroporous conjugated polymers are synthesized via in situ growth of poly(3-hexylthiophene) (P3HT) from reduced graphene oxide (RGO) sheets, followed by gelation of the composite (RGO-g-P3HT) in p-xylene and freeze-drying. The network structures of the macroporous materials can be readily tuned by controlling the chain length of P3HT grafted to RGO sheets. The large pore volumes of the macroporous RGO-g-P3HT materials (ca. 34 cm3 g–1) make them excellent frameworks for hosting sulfur as cathodes o...

We have developed new polymer optical interconnect materials that we term refractive index contrast (RIC) polymers that are ideally suited to a wide variety of photonic interconnect applications as the refractive index can be tuned over the range of n = 1.42 to 1.56, while index contrast Δn can be precisely tuned through composition and ultraviolet exposure; the waveguides can be directly patterned in dry films with no wet or dry etching processes required. RIC polymer interconnects thus have the ability to access numerous photonic platforms, including silicon photonic chips, ion-exchange (IOX) glass optical substrates, and optical fiber arrays. We demonstrate for the first time efficient single-mode polymer interconnect fabrication via a maskless lithography approach that exhibits low loss adiabatic coupling (∼1.5dB at 1550nm) to IOX waveguides through the formation of grayscale tapers.

Colorless, transparent polymer thin films with n > 1.9 were prepared through vapor deposition polymerization of elemental sulfur., High refractive index polymers (HRIPs) have recently emerged as an important class of materials for use in a variety of optoelectronic devices including image sensors, lithography, and light-emitting diodes. However, achieving polymers having refractive index exceeding 1.8 while maintaining full transparency in the visible range still remains formidably challenging. Here, we present a unique one-step vapor-phase process, termed sulfur chemical vapor deposition, to generate highly stable, ultrahigh refractive index (n > 1.9) polymers directly from elemental sulfur. The deposition process involved vapor-phase radical polymerization between elemental sulfur and vinyl monomers to provide polymer films with controlled thickness and sulfur content, along with the refractive index as high as 1.91. Notably, the HRIP thin film showed unprecedented optical transparency throughout the visible range, attributed to the absence of long polysulfide segments within the polymer, which will serve as a key component in a wide range of optical devices.

Small-molecule catalysts inspired by the active sites of [FeFe]-hydrogenase enzymes have long struggled to achieve fast rates of hydrogen evolution, long-term stability, water solubility, and oxyge...

In this report, a new class of functional chalcogenide hybrid inorganic/organic polymers (CHIPs) bearing free aryl amine groups that are amenable to post-polymerization modifications were synthesized. These functional CHIPs were synthesized via the inverse vulcanization of elemental sulfur with 4-vinylaniline without the need for functional group protection of amines. This polymer is the first example of a polysulfide or CHIP material to carry a useful primary amine functional group which can be successfully post functionalized with acid chlorides and isocyanates to improve the mechanical properties.

Force modulation microscopy (FMM) is a mode of scanning probe microscopy that can be used to visualize changes of tip–sample interactions for hard and soft areas of samples such as polymers and organic thin films. In designed experiments, polystyrene-encapsulated cobalt nanoparticles were imaged with FMM using a home-built sample stage for sample actuation. Regions of the outer polymer coating and the inner cobalt nanoparticle were resolved with high resolution. Using FMM, differences in the elastic and viscoelastic properties of the nanoparticles were visualized with nanoscale resolution by monitoring the return amplitude and phase signals as the AFM tip is scanned over areas of a sample. Regions of the sample with greater elasticity and viscoelasticity generate a weaker signal relative to harder areas because more of the energy associated with the cantilever oscillation is dissipated by the material. Areas with greater elasticity will tend to absorb more of the energy of the cantilever causing the ampli...

We report on the preparation of ultrahigh refractive index polymers via the inverse vulcanization of elemental sulfur, selenium, and 1,3-diisopropenylbenzene for use as novel transmissive materials for mid-infrared (IR) imaging applications. Poly(sulfur-random-selenium-random-(1,3-diisopropenylbenzene)) (poly(S-r-Se-r-DIB) terpolymer materials from this process exhibit the highest refractive index of any synthetic polymer (n > 2.0) and excellent IR transparency, which can be directly tuned by terpolymer composition. Sulfur or selenium containing (co)polymers prepared via inverse vulcanization can be described as Chalcogenide Hybrid Inorganic/Organic Polymers (CHIPs) and are polymeric analogues to wholly inorganic Chalcogenide Glasses (ChGs), which are commonly used as transmissive materials in mid-IR imaging. Finally, we demonstrate that CHIPs composed of (poly(S-r-Se-r-DIB) can be melt processed into windows that enabled high quality mid-IR thermal imaging of human subjects and highly resolved imaging of...

Recent developments in the use of polymeric materials as device components in lithium sulfur (Li-S) batteries are reviewed. Li-S batteries have generated tremendous interest as a next generation battery exhibiting charge capacities and energy densities that greatly exceed Li-ion battery technologies. In this Highlight, the first comprehensive review focusing on the use of polymeric materials throughout these devices is provided. The key role polymers play in Li-S technology is presented and organized in terms of the basic components that comprise a Li-S battery: the cathode, separator, electrolyte, and anode. After a straightforward introduction to the construction of a conventional Li-S device and the mechanisms at work during cell operation, the use of polymers as binders, protective coatings, separators, electrolytes, and electroactive materials in Li-S batteries will be reviewed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1635–1668

We report on the preparation and modification of chalcogenide hybrid inorganic/organic polymer (CHIPs) via the inverse vulcanization of elemental sulfur with styrenics to afford low glass transition (Tg) copolymers. Furthermore, poly(sulfur-random-styrene) (poly(S-r-Sty)) can be further utilized as reactive liquid resins that are miscible with a wider range of styrenic, acrylate and allylic comonomers. We describe a new process termed, dynamic covalent polymerization (DCP), where the dynamic S–S bonds in poly(S-r-Sty) liquid polysulfides were thermally activated to generate sulfur radicals that added to vinylic comonomers to prepare novel terpolymer CHIPs. Using this sequential process we demonstrate the ability to incorporate functional comonomers that were otherwise immiscible with liquid sulfur.

We report on noble metal tipping of heterostructured nanocrystals (NCs) of CdSe@CdS tetrapods (TPs) as a chemical reaction to manifest energetic differences between type I and quasi-type II heterojunctions. The energetics between zincblende (ZB) CdSe seed and wurtzite CdS TP arms has previously been probed primarily using ultrafast spectroscopic methods. However, to interrogate the energetics of CdSe@CdS TPs from both larger and very small ZB CdSe seeds (i.e., effective diameters (Deff) 6.2 to 1.8 nm) we utilize the photodeposition of gold nanoparticles as a facile and selective chemical reaction to correlate reaction rates with tetrapod energetics. We observe a 20-fold enhancement in the rate of selective photodeposition of a single AuNP tip onto this series of TPs, which were attributed to straddling of type I vs. quasi-type II energetics as a direct consequence of varying ZB CdSe seed size. Synthetic access to type I and quasi-type II TPs enabled the synthesis of singly tipped AuNP-CdSe@CdS TPs in gram quantities, which is the largest scale synthesis of metal–semiconductor Janus nanoparticles to date.

For the first time, a high sulfur content polymer has been photo-bleached to yield an optical waveguide suitable for mid-wave infrared (MWIR) photonics. The polymer was synthesized by inverse vulcanization of elemental sulfur with the organic monomer 1,3-diisopropenylbenzene (DIB) to produce the polymeric material poly(sulfur-r-(1,3-diisopropenylbenze)) (poly(s-r-DIB)). This glassy, red polymer is available in bulk/solution form and affords easy processability. This novel polymer is extremely low cost, displays high refractive index (1.8), and is transparent at most short-wave infrared (SWIR) and MWIR wavelengths. These attributes make it highly desirable and a more suitable substitute to commercially available alternatives, such as chalcogenide glasses, which can be toxic, expensive and difficult to process. In this work, we demonstrate that photo-bleaching of the polymer occurs when exposed to intense UV light, inducing a change in the refractive index. The index can thereby also be tuned by changing the exposure parameters and the ambient atmospheric conditions. This phenomenon was used to fabricate optical waveguides suitable for SWIR and MWIR wavelengths. Optical characterization of the waveguides was performed to measure the propagation losses of the material. The low cost of the material and the facile nature of the fabrication and processing enables high reproducibility making this system desirable for a multitude of photonic applications such as on-chip spectroscopy and frequency combs.

Poly[sulfur-random-(1,3-diisopropenylbenzene)] copolymers synthesized via inverse vulcanization represent an emerging class of electrochemically active polymers recently used in cathodes for Li–S batteries, capable of realizing enhanced capacity retention (1,005 mAh/g at 100 cycles) and lifetimes of over 500 cycles. The composite cathodes are organized in complex hierarchical three-dimensional (3D) architectures, which contain several components and are challenging to understand and characterize using any single technique. Here, multimode analytical scanning and transmission electron microscopies and energy-dispersive X-ray/electron energy-loss spectroscopies coupled with multivariate statistical analysis and tomography were applied to explore origins of the cathode-enhanced capacity retention. The surface topography, morphology, bonding, and compositions of the cathodes created by combining sulfur copolymers with varying 1,3-diisopropenylbenzene content and conductive carbons have been investigated at multiple scales in relation to the electrochemical performance and physico-mechanical stability. We demonstrate that replacing the elemental sulfur with organosulfur copolymers improves the compositional homogeneity and compatibility between carbons and sulfur-containing domains down to sub-5 nm length scales resulting in (a) intimate wetting of nanocarbons by the copolymers at interfaces; (b) the creation of 3D percolation networks of conductive pathways involving graphitic-like outer shells of aggregated carbons; (c) concomitant improvements in the stability with preserved meso- and nanoscale porosities required for efficient charge transport.

Copolymerization of liquid sulfur with 1,3-di-isopropenylbenzene in the absence of any organic solvent provides a stable copolymer which can be cast in molds and also forms a transparent glass. Thi...

The synthesis of a novel high sulfur content material possessing improved thermomechanical properties is reported via the inverse vulcanization of elemental sulfur (S8) and 1,3,5-triisopropenylbenzene (TIB). A key feature of this system was the ability to afford highly cross-linked, thermosetting materials, where the use of TIB as a comonomer enabled facile control of the network structure and dramatically improved the glass transition temperature (relative to our earlier sulfur copolymers) of poly(sulfur-random-(1,3,5-triisopropenylbenzene)) (poly(S-r-TIB)) materials over a range from T = 68 to 130 °C. This approach allowed for the incorporation of a high content of sulfur–sulfur (S–S) units in the copolymer that enabled thermomechanical scission of these dynamic covalent bonds and thermal reprocessing of the material, which we confirmed via dynamic rheological characterization. Furthermore, the high sulfur content also imparted high refractive index (n > 1.75) and IR transparency to poly(S-r-TIB) copoly...

High sulfur content copolymers were prepared via the inverse vulcanization of elemental sulfur with styrene. This reaction was carried out at a relatively low temperature and invokes a new chain transfer mechanism of abstraction of benzylic protons to form stable copolymers. The use of styrene as a comonomer for inverse vulcanization was attractive due to the low cost and wide spread industrial use of styrenics in free radical processes. The copolymers were used as the active cathode material in Li-S batteries that exhibited outstanding device performance, maintaining 489 mAh/g capacity after 1000 cycles. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 107–116

We report on a versatile synthetic method of preparing colloidal copolymers and terpolymers composed of dipolar Au@Co core-shell nanoparticles (NPs) in the backbone, along with semiconductor CdSe@CdS nanorod (NR), or tetrapod (TP) side chain groups. A seven-step colloidal total synthesis enabled the synthesis of well-defined colloidal comonomers composed of a dipolar Au@CoNP attached to a single CdSe@CdS NR, or TP, where magnetic dipolar associations between Au@CoNP units promoted the formation of colloidal co- or terpolymers. The key step in this synthesis was the ability to photodeposit a single AuNP tip onto CdSe@CdS NR or TP that enables selective seeding of a dipolar CoNP onto the AuNP seed. We show that the variation of the AuNP size directly controlled the size and dipolar character of the CoNP tip, where the size modulation of the Au and Au@CoNP tips is analogous to control of comonomer reactivity ratios in classical copolymerization processes.

Pt-decorated CdSe tetrapods with different arm lengths were tested for the photocatalytic hydrogen generation reaction. Well-defined CdSe tetrapods with controlled wurtzite arm lengths were synthesized by the continuous precursor injection (CPI) approach. Pt nanocrystals with an extremely small size of ∼1 nm were directly decorated on the overall surfaces of CdSe tetrapods. Ligand-exchanged Pt-decorated CdSe tetrapods with different arm lengths were employed as photocatalysts for photocatalytic hydrogen generation reaction in the presence of hole scavengers. Pt-decorated CdSe tetrapods with shorter arm length showed the highest photocatalytic efficiency, which is due to higher probability of charge separation.