Patent Application: US-201214115663-A

Abstract:
in this invention , we disclose a method as well as silica and / or organosilica mesoporous materials obtained by templating using nanocrystalline cellulose and removal of the latter using acidic conditions . the resultant mesoporous silica materials are characterized by having high surface area with tunable iridescence resulting from the long - range chiral nematic organization . this invention is an improvement over the formation of composite materials formed with nanocrystalline cellulose and silica , where the calcination of the materials led to removal of the cellulose and formation of a mesoporous silica material . characteristically , the removal of the ncc template using acidic conditions differentiates the silica materials thus obtained in two ways : it does not lead to as significant contraction of the materials as from calcination thereby giving access to materials with larger mesopores ; and it allows the formation of mesoporous chiral nematic compositions that include heat - sensitive components . this approach may be used to prepare the first example of a mesoporous organosilica material with a chiral nematic pore structure . examples of possible applications of this material include optical filters , adsorbents , chiral stationary phases for chromatography , sensors , composite materials , membranes , and templates for creating other chiral materials .

Description:
a new process for generating mesoporous materials from organosilica / ncc and silica / ncc composites ( where ncc is nanocrystalline cellulose ) by removing the ncc using acidic solutions has been developed . this gives rise to mesoporous materials that may be obtained as free - standing films with chiral nematic organization . compared to the prior art processes that use high temperature treatments to remove ncc , this process yields materials with larger mesopores . furthermore , it gives access to the first examples of mesoporous organosilicas templated by ncc , which cannot generally be synthesized through calcination due to the thermal or oxidative sensitivity of the organic groups . this process allows for a completely novel material to be synthesized , namely mesoporous organosilica templated by cellulose , which cannot be synthesized by calcination of an organosilica / ncc composite material . furthermore the process results in mesoporous siliceous materials exhibiting higher peak pore diameter as compared with corresponding mesoporous siliceous materials produced under conditions of calcination for removal of ncc . the mesoporous materials may be produced as films which may have chiral or achiral structure . in the case of films with chiral nematic structure , such structure results in iridescence , the color of which may be tuned by changing the ratio of organosilica precursor to ncc . this provides the first example of mesoporous organosilicas with chiral nematic structures . the invention also allows for preparation of silica - ncc and organosilica - ncc composites that do not have the chiral nematic structure , the acid treatment method described herein may be applied to such materials to afford porous silica or organosilica with or without chiral nematic organization . the combination of porosity and optical properties in these materials makes them interesting for a wide range of applications . the invention employs a new method for the removal of cellulose from silica / ncc or organosilica / ncc composites using aqueous acids that leads to mesoporous silica or organosilica materials . these new mesoporous materials have significantly different properties compared to the corresponding materials obtained when the ncc is removed by calcination . this process enables the development of materials with temperature - sensitive components that would be degraded during thermal decomposition of the ncc . also , it enables access to different pore sizes than those obtained from thermal decomposition of ncc . in particular , by utilizing acid hydrolysis of ncc from chiral nematic organosilica / ncc composites , novel mesoporous organosilica materials with chiral nematic structures can be prepared . nitrogen adsorption isotherms show that the materials obtained have high surface areas and porosity . these novel materials are attractive for many practical applications , including catalyst supports ( possibly including enantioselective transformations ), stationary phases ( for separation of chiral or achiral substances ), optical filters , sensors , insulators , adsorbents , membranes , and as templates for other chiral nanomaterials . the invention provides the process to remove ncc from silica / ncc or organosilica / ncc composites , as well as the novel materials obtained after removal of the ncc , including both chiral nematic and achiral structures . the acid hydroysis in the process of the invention is typically carried out with maintenance of pores of a volume corresponding to the volume of the composite occupied by the nanocrystalline cellulose ( ncc ). in particular the composite comprises a siliceous matrix surrounding a skeleton of ncc crystals in which the crystals occupy a volume in the composite defining potential mesopores , i . e . the mesopores left after removal of the cellulose by the acid hydrolysis . in particular the mesopores have a peak pore diameter higher than that of a corresponding mesoporous siliceous material produced by calcination of cellulose of the composite and more especially have mesopores with a peak pore diameter of at least 5 nm , and typically 5 to 15 nm . the acid hydrolysis is typically carried out with a concentrated acid , for example hydrochloric acid , sulphuric acid , nitric acid or trifluoromethanesulfonic acid . the acid concentration should generally be greater than 3m and more usually greater than 6m . in the case of hydrochloric acid it is especially preferred to have a concentration of 10 to 12m and more especially about 12m . in the case of sulphuric acid a concentration of 4m to 8m and especially about 6m is preferred . nanocrystalline cellulose ( ncc ) is extracted as a colloidal suspension by acid hydrolysis of cellulosic materials , derived from sources such as bacteria , cotton , and wood pulp . ncc is made from cellulose , a linear polymer of β ( 1 → 4 ) linked d - glucose units , the chains of which arrange themselves to form crystalline and amorphous domains . the ncc is extracted by selectively hydrolyzing the amorphous regions leaving behind the highly crystalline ncc . ncc is characterized by high crystallinity ( between 85 and 97 %, typically greater than 95 %) approaching the theoretical limit of the cellulose chains . colloidal suspensions of cellulose crystallites form a chiral nematic structure upon reaching a critical concentration . the chiral nematic structure of ncc suspensions may be preserved upon evaporation , resulting in chiral nematic films where the helicoidal axis is oriented perpendicular to the surface of the films . these films are visibly iridescent when the helical pitch is on the order of the wavelengths of visible light . a broad range of silica and organosilica precursors , e . g . of the general types si ( or ) 4 , si ( or 1 ) 3 r , and si ( or 1 ) 3 r 2 si ( or 3 ) 3 , and mixtures thereof in which each r , r 1 and r 3 may be the same or different and is typically a phenyl group ( c 6 h 5 ), a substituted phenyl group , an alkyl group , a branched alkyl group , a cycloalkane , or any similar organic component , and r 2 is a bridging organic component , such as 1 , 4 - phenylene ( c 6 h 4 ), methylene ( ch 2 ), ethylene ( ch 2 ch 2 ), propylene ( ch 2 ch 2 ch 2 ), or any other linear or branched alkylene spacer ( e . g ., ( ch 2 ) 6 ), may be condensed in the presence of ncc to form organosilica / ncc or silica / ncc composite materials . under appropriate conditions , these composite materials may be obtained as free - standing or self - supporting films with long - range chiral nematic structures . the full synthesis and characterization of chiral nematic silica / ncc composite films has been described in u . s . patent application ser . no . 13 / 076 , 469 filed mar . 31 , 2011 , and the contents thereof are incorporated herein by reference . in the present invention , organosilica / ncc and silica / ncc composite materials such as are described in the aforementioned earlier us patent application are subjected to different acidic conditions in order to obtain mesoporous materials , which may be obtained as free - standing films with long - range chiral nematic structures . the removal of ncc from free - standing chiral nematic silica / ncc composite films ( preparation 1 ) may be successfully carried out with inorganic acids , for example hydrochloric acid , sulfuric acid , or nitric acid , or mixtures thereof . treatment of the films in concentrated acid in water is typically at elevated temperatures in the range of 70 ° c . to 120 ° c . acid hydrolysis with hydrochloric acid in water ( 12 m ) at elevated temperatures ( preferably & gt ; 80 ° c .) and ambient pressure causes decomposition of the ncc within the composite films ( when concentrated hcl is used at lower concentrations or temperatures , ncc degradation does not appear to occur ). free - standing mesoporous silica films are obtained after filtration and washing with water ( preparation 2 ). initially colorless films with a reflectance peak ( measured by uv - visible spectroscopy ) at 1260 nm ( fig1 ) owing to the chiral nematic structure of the films appear light to dark brown after the hcl treatment due to the formation of insoluble cellulose decomposition products . a reflection peak is apparent in the dry films at 700 nm ( fig2 ) demonstrating that the chiral nematic structure is retained in the films after the acid treatment . the blue - shift in the reflectance peak is consistent with the decrease in refractive index that occurs due to cellulose removal . the infrared ( ir ) spectrum ( fig3 ) of the product obtained from preparation 2 confirms that cellulose decomposition has occurred . however , as indicated by the brown color of the films and thermogravimetric analysis ( tga ) ( fig4 ), residual organic material ( 22 wt . %) with a decomposition temperature of ˜ 400 ° c . is still present in the material . nitrogen adsorption measurements reveal a type iv isotherm with hysteresis demonstrating that the films are mesoporous ( bet , brunauer - emmett - teller model , surface area = 470 m 2 / g , fig5 ). significantly , the pore diameter is considerably larger than the analogous materials prepared by calcination of the silica - ncc composite material . the bjh ( barret - joyner - halenda model ) pore size distribution shows a peak pore diameter of 7 nm ( fig6 ). ( the peak pore diameter for samples prepared directly by calcination is typically & lt ; 4 nm .) the residual organic material may be removed from the films using oxidizing conditions ( preparation 3 ). when the brown mesoporous films are placed in a 4 : 1 mixture of sulfuric acid and hydrogen peroxide ( 30 % in water ), the color rapidly disappears . after washing the films with water and drying , the films regain their iridescence and show a reflectance peak at 680 nm ( fig7 ) that is attributed to the chiral nematic structure . the reflectance peak is located at essentially the same position that was observed before the oxidizing treatment ; however , it is much more distinct due to the removal of the brown organic contaminants . ir spectroscopy ( fig8 ) and tga ( fig9 ) confirm that the oxidizing treatment is able to successfully remove the residual cellulose decomposition products from the films . elemental analysis reveals only trace amounts of carbon after the oxidizing treatment (& lt ; 0 . 3 wt . %). nitrogen adsorption shows that this treatment does not substantially affect the porosity of the materials , with the isotherm ( fig1 ) and bjh pore size distribution ( fig1 ) essentially unchanged . the specific pore volume is slightly increased , which is consistent with the removal of residual organic material from the mesopores . scanning electron microscopy ( sem ) provides further evidence that long range chiral nematic order is maintained in the mesoporous silica obtained using preparation 3 ( fig1 ). at higher magnification the rod - like morphology of ncc imprinted into the silica ( fig1 ) is observed . the mesoporous silica is therefore an accurate replica of the ncc template . this demonstrates that this procedure is able to selectively remove ncc without causing structural damage to the silica . sulfuric acid may also be employed to remove ncc from the composite films . treatment of the composite films in 6 - 9 m sulfuric acid at & gt ; 80 ° c . ( preparation 4 ) also results in slightly brown mesoporous silica films . the reflection peak observed in the uv - vis spectrum ( 690 nm , fig1 ) is very similar to that observed for preparations 2 and 3 ; however , the porosity ( fig1 - 16 ) measured for preparation 4 is somewhat different . while the peak bjh pore diameter is very similar (˜ 7 nm ) the bet surface area ( 750 m 2 / g ) is considerably higher than that measured for preparations 2 and 3 . ir spectroscopy ( fig1 ) and tga ( fig1 ) reveal that considerably less residual cellulosic decomposition products remain in the films compared to when concentrated hcl is used . sulfuric acid / hydrogen peroxide can also be successfully used to completely remove any remaining insoluble cellulosic decomposition products from preparation 4 . concentrated nitric acid at 85 ° c . ( preparation 5 ) also removes ncc from the composite films . however , the reflectance peak ( from the chiral nematic structure ) and porosity measured for this sample are considerably different than those measured for preparations 2 , 3 , and 4 . the reflectance peak for preparation 5 is blue - shifted compared to preparations 2 and 4 and occurs at 560 nm ( fig1 ). the bet surface area measured for the material obtained from preparation 5 is still high ( 450 m 2 / g ), but the shape of the n 2 adsorption / desorption isotherm ( type i / 1v hybrid ) indicates that there is a large micropore contribution to the surface area ( fig2 ). the bjh pore size - distribution gives a sharp peak at 3 . 5 nm ( fig2 ), which is approximately half the diameter of those calculated for preparations 2 - 4 . it therefore appears that in contrast to hydrochloric acid and sulphuric acid , nitric acid causes structural damage to the mesoporous silica framework . this may be avoidable by adjusting the concentration and temperature employed in the procedure . organosilica - ncc composite films were prepared using 1 , 2 - bis ( triethoxysilyl )- ethane as the organosilica precursor ( preparations 6 and 8 ). preparation 6 gives free - standing films with a chiral nematic structure as indicated by a reflectance peak at 620 nm ( fig2 ) in the uv - visible spectrum . these films were studied to determine whether acid hydrolysis can be used to generate mesoporous organosilica from organosilica - ncc composites ; i . e ., whether ncc can be selectively removed from the composite without decomposition of the organosilica . the composite material was subjected to concentrated hcl at 85 ° c . followed by brief treatment with h 2 so 4 / hydrogen peroxide ( preparation 7 ) in order to ensure complete removal of ncc and any cellulosic decomposition products . this treatment results in somewhat flexible , iridescent , free - standing films . after cellulose removal , the reflectance peak in the uv - visible spectrum is shifted to 450 nm ( fig2 ). ir spectroscopy , tga , and elemental analysis confirm that the cellulose is removed with retention of the ethylene bridge in the organosilica . the ir spectrum ( fig2 ) shows peaks at 1270 cm − 1 and 690 cm − 1 corresponding to si — c symmetric deformation and stretching respectively , while two peaks corresponding to ch 2 stretching modes are seen at 2895 cm − 1 and 2930 cm − 1 . from tga , a 20 % wt . loss is observed at 450 ° c . ( fig2 ), matching very closely to the theoretical value of 21 % based on the loss of c 2 h 4 from a material with the chemical formula c 2 h 4 o 3 si 2 . elemental analysis gives a value of 17 . 3 % carbon , which is again very close to the theoretical value of 18 . 2 % based on the above formula . n 2 adsorption shows the organosilica to be mesoporous with a very similar isotherm to that measured for the mesoporous silica prepared using the same procedure ( fig2 ). indeed the bet surface area ( 460 m 2 / g ) and peak pore size ( 7 nm , fig2 ) are virtually identical to the values calculated for the mesoporous silica prepared using the same conditions ( preparation 3 ). sem images show a chiral nematic structure that is an accurate replica of the ncc template ( fig2 - 29 ). generally , the free - standing mesoporous organosilica films appear similar to the corresponding mesoporous silica films , however , the organosilica films are considerably less brittle and more flexible . these superior mechanical properties could be advantageous for certain applications . an additional mesoporous organosilica sample was prepared in order to demonstrate that the color of the films can be tuned in the same way as chiral nematic mesoporous silica films ( i . e ., by varying the ratio of ncc and silica precursor ). preparation 8 is identical to preparation 6 except that a higher ratio of 1 , 2 - bis ( triethoxysilyl )- ethane was used relative to ncc . as expected , the reflectance peak for this sample is red - shifted ( λ max = 820 nm ) compared to the sample prepared in preparation 6 ( fig3 ). following the same procedure as preparation 7 , the ncc from the composite films may be removed while leaving the organosilica intact , resulting in mesoporous organosilica films with a peak reflectance of 680 nm ( preparation 9 , fig3 ). the color of the mesoporous organosilica films may therefore be tuned by varying the ratio of organosilica precursor to ncc used in the synthesis . preparations 10 through 19 show further examples of organosilica / ncc composites and the corresponding mesoporous organosilica materials , all with chiral nematic organization as evidenced by iridescence and a reflection peak in the uv - visible / near - ir spectrum . these illustrate that the organic component in the matrix may be varied to obtain the chiral nematic organosilica / ncc composites and mesoporous organosilica materials . thus , in accordance with the invention ncc may be selectively removed from silica / ncc or organosilica / ncc composites using acid - catalyzed hydrolysis . the vast literature of pre - treatment methods that are known to improve the efficiency of acid - catalyzed cellulose hydrolysis ( e . g . hydrothermal , ozonolysis , etc .) should also be applicable to the process of the invention , given the stabilities of silica and organosilica materials . for both silica and organosilica , the resulting mesoporous materials may be obtained as free - standing chiral nematic films with larger mesopores than the corresponding materials obtained by calcination . this process allows for a completely novel material to be synthesized , namely mesoporous organosilica templated by ncc , which cannot be synthesized by calcination of an organosilica - ncc composite material . the chiral nematic structure of these films results in iridescence , the color of which may be tuned by changing the ratio of organosilica precursor to ncc . silica - ncc and organosilica - ncc composites can also be prepared that do not have the chiral nematic structure , the acid treatment method described herein may be applied to such materials to afford porous silica or organosilica with or without chiral nematic organization . the combination of porosity and optical properties in these materials makes them interesting for a wide range of applications . in the examples , sonication was applied to ensure that the ncc particles were dispersed . the sonicator was a standard laboratory model ( 2 a , 120 v ) available from vwr ( aquasonic model 50t — trademark ). a sonication time of 10 - 15 minutes was typically applied prior to addition of the silicon - containing compound . 4 ml of tetramethoxysilane ( tmos ) is added to 100 ml of a freshly sonicated 3 . 5 % aqueous suspension of ncc . the mixture is stirred for 1 h at 20 ° c . and then poured into polystyrene petri dishes to evaporate . the resulting colorless films are peeled off of the substrate to obtain free - standing composite films with a reflectance peak at 1260 nm ( fig1 ). silica / ncc composite films from preparation 1 ( 411 mg ) are added to 500 ml of 12 m hcl and heated to 85 ° c . for 18 h . after cooling to room temperature , the reaction mixture is poured into 1 l of water and filtered . the recovered films are washed with water and after drying , 216 mg of light brown / iridescent films with a reflectance peak at 700 nm ( fig2 ) are obtained . the ir spectrum ( fig3 ) and tga ( fig4 ) of the sample show that ncc decomposition has occurred with some residual organic material remaining in the films . n 2 adsorption measurements ( fig5 ) give a bet surface area of 470 m 2 / g and a specific pore volume of 0 . 68 cm 3 / g . mesoporous silica films from preparation 2 ( 150 mg ) are placed in 100 ml of 4 : 1 h 2 so 4 / hydrogen peroxide ( 30 %) until the films are completely colorless (˜ 5 min ). the reaction mixture is poured into 1 l of water and filtered . the recovered films are washed with water and after drying , 120 mg of iridescent films with a reflectance peak at 680 nm ( fig7 ) are obtained . the ir spectrum ( fig8 ), elemental analysis , and tga ( fig9 ) of the sample show that all organic material has been removed . n 2 adsorption measurements ( fig1 ) give a bet surface area of 450 m 2 / g and a specific pore volume of 0 . 77 cm 3 / g . silica / ncc composite films from preparation 1 ( 400 mg ) are added to 160 ml of 9m h 2 so 4 and heated to 85 ° c . for 18 h . after cooling to room temperature , the reaction mixture is poured into 1 l of water and filtered . the recovered films are washed with water and after drying , 160 mg of mostly colorless iridescent films with a reflectance peak at 680 nm ( fig1 ) are obtained . the ir spectrum ( fig1 ) and tga ( fig1 ) of the sample show that the ncc has been removed from the films . n 2 adsorption measurements ( fig1 ) give a bet surface area of 750 m 2 / g and a specific pore volume of 0 . 92 cm 3 / g . silica / ncc composite films from preparation 1 ( 400 mg ) are added to 160 ml of concentrated nitric acid and heated to 85 ° c . for 18 h . after cooling to room temperature , the reaction mixture is poured into 1 l of water and filtered . the recovered films are washed with water and after drying , 130 mg of iridescent films with a reflectance peak at 560 nm ( fig1 ) are obtained . the ir spectrum and tga of the sample show that the ncc has been removed from the films . n 2 adsorption measurements ( fig2 ) give a bet surface area of 450 m 2 / g and a specific pore volume of 0 . 30 cm 3 / g . 1 . 28 ml of 1 , 2 - bis ( triethoxysilyl )- ethane is added to 20 ml of a freshly sonicated 3 % aqueous suspension of ncc . the mixture is stirred for 3 h at 90 ° c . and then left stirring at 20 ° c . for 18 h . the reaction mixture is microfiltered ( 0 . 45 μm ) and poured into polystyrene petri dishes to evaporate . the resulting iridescent films are peeled off of the substrate to obtain free - standing composite films with a reflectance peak at 620 nm ( fig2 ). organosilica / ncc composite films from preparation 6 ( 360 mg ) are placed in 400 ml of 12 m hcl and heated to 85 ° c . for 18 h . after cooling to room temperature , the reaction mixture is poured into 1 l of water and filtered . after washing with water and drying , the slightly brown iridescent films are placed in 50 ml of 4 : 1 h 2 so 4 / h 2 o 2 ( 30 %) until the films are completely colorless (˜ 2 - 3 min ). the reaction mixture is poured into 500 ml of water , filtered , and washed with water . after air - drying , 160 mg of iridescent films with a reflection peak at 450 nm ( fig2 ) are obtained . ir spectroscopy ( fig2 ), tga ( fig2 ), and elemental analysis confirm that the cellulose is removed with retention of the ethylene bridge in the organosilica . n 2 adsorption measurements ( fig2 ) give a bet surface area of 460 m 2 / g and a specific pore volume of 0 . 73 cm 3 / g . 1 . 70 ml of 1 , 2 - bis ( triethoxysilyl )- ethane is added to 20 ml of a freshly sonicated 3 % aqueous suspension of ncc . the mixture is stirred for 3 h at 90 ° c . and then left stirring at 20 ° c . for 18 h . the reaction mixture is microfiltered ( 0 . 45 μm ) and poured into polystyrene petri dishes to evaporate . the resulting iridescent films are peeled off of the substrate to obtain free - standing composite films with a reflectance peak at 820 nm ( fig3 ). organosilica / ncc composite films from preparation 8 ( 584 mg ) are placed in 400 ml of 12 m hcl and heated to 85 ° c . for 18 h . after cooling to room temperature , the reaction mixture is poured into 1 l of water and filtered . after washing with water and drying , the slightly brown iridescent films are placed in 50 ml of 4 : 1 h 2 so 4 / h 2 o 2 ( 30 %) until the films are completely colorless (˜ 2 - 3 min ). the reaction mixture is poured into 500 ml of water , filtered , and washed with water . after air - drying , 270 mg of iridescent films with a reflection peak at 680 nm ( fig3 ) are obtained . ir spectroscopy , tga , and elemental analysis confirm that the cellulose is removed with retention of the ethylene bridge in the organosilica . n 2 adsorption measurements give a bet surface area of 498 m 2 / g and a specific pore volume of 0 . 80 cm 3 / g . 0 . 5 ml of 1 , 2 - bis ( trimethoxysilyl )- ethane is added to 15 ml of 3 . 5 % aqueous ncc . the mixture is stirred for 2 h at room temperature . the reaction mixture is poured into polystyrene petri dishes to evaporate . the resulting iridescent films are peeled off of the substrate to obtain free - standing composite films with a reflectance peak at ˜ 1160 nm . organosilica / ncc composite films from preparation 10 are placed in 6m h 2 so 4 and heated to 100 ° c . for 20 hours . after cooling to room temperature , the reaction mixture was filtered and alternately washed with a solution of piranha ( 20 ml 30 % h 2 o 2 / 100 ml h 2 so 4 ) and water until colorless . the films were then washed with water and allowed to air - dry . 130 mg of the iridescent films with a reflection peak at ˜ 720 nm are obtained . ir spectroscopy and tga confirmed that the cellulose is removed with retention of the ethylene bridge in the organosilica . n 2 adsorption measurements indicate a mesoporous material with a bet surface area of 594 m 2 / g and a specific pore volume of 0 . 87 cm 3 / g . 0 . 47 ml of 1 , 2 - bis ( triethoxysilyl )- methane is added to 10 ml of 3 . 5 % aqueous ncc and 4 ml of ethanol . the mixture is stirred for 2 h at room temperature . the reaction mixture is poured into polystyrene petri dishes to evaporate . the resulting iridescent films are peeled off of the substrate to obtain free - standing composite films with a reflectance peak at − 1215 nm . organosilica / ncc composite films from preparation 12 are placed in 6m h 2 so 4 and heated to 100 ° c . for 20 hours . after cooling to room temperature , the reaction mixture was filtered and alternately washed with a solution of piranha ( 20 ml 30 % h 2 o 2 / 100 ml h 2 so 4 ) and water until colorless . the films were then washed with water and allowed to air - dry . 101 mg of the iridescent films with a reflection peak at ˜ 670 nm are obtained . ir spectroscopy , tga , and elemental analysis confirmed that the cellulose is removed with retention of the methylene bridge in the organosilica . n 2 adsorption measurements show the material is mesoporous with a bet surface area of 518 m 2 / g and a specific pore volume of 0 . 54 cm 3 / g . 1 . 2 ml of 1 , 4 - bis ( triethoxysilyl )- benzene is added to 35 ml of freshly sonicated 3 . 5 % aqueous ncc and 35 ml of ethanol . the mixture is stirred for 2 h at room temperature . the reaction mixture is poured into polystyrene petri dishes to evaporate . the resulting iridescent films are peeled off of the substrate to obtain free - standing composite films with a reflectance peak at ˜ 1470 nm . organosilica / ncc composite films from preparation 14 are placed in concentrated hcl and heated to 90 ° c . for 20 hours . the films were filtered , washed with water and placed in a solution of hydrogen peroxide ( 30 %, 20 ml ) and silver nitrate ( 0 . 013 g ) at 90 ° c . for 2 hours . the films were then filtered , placed in water and heated to 70 ° c . overnight . the films were filtered and allowed to air - dry . 73 mg of the iridescent films with a reflection peak at ˜ 665 nm are obtained . ir spectroscopy and tga confirmed that the cellulose is removed with retention of the benzene bridge in the organosilica . 0 . 24 ml of 1 , 2 - bis ( trimethoxysilyl )- ethane and 0 . 13 ml of 1 , 6 - bis ( trimethoxysilyl )- hexane is added to 10 . 2 ml of 3 . 5 % aqueous ncc . the mixture is stirred for 2 h at room temperature . the reaction mixture is poured into polystyrene petri dishes to evaporate . the resulting iridescent films are peeled off of the substrate to obtain free - standing composite films with a reflectance peak at ˜ 1215 nm . organosilica / ncc composite films from preparation 16 are placed in 6m h 2 so 4 and heated to 100 ° c . for 20 hours . after cooling to room temperature , the reaction mixture was filtered and alternately washed with a solution of piranha ( 20 ml 30 % h 2 o 2 / 100 ml h 2 so 4 ) and water until colorless . the films were then washed with water and allowed to air - dry . 70 mg of the iridescent films with a reflection peak at 700 - 750 nm are obtained . ir spectroscopy , tga , and elemental analysis confirmed that the cellulose is removed with retention of the ethylene and hexane bridges in the organosilica . n 2 adsorption measurements indicate that the material is mesoporous with a bet surface area of 467 m 2 / g and a specific pore volume of 0 . 78 cm 3 / g . 0 . 47 ml of 1 , 2 - bis ( trimethoxysilyl )- ethane and 0 . 32 ml of 1 , 4 - bis ( triethoxysilyl )- benzene is added to 20 ml of freshly sonicated 3 . 5 % aqueous ncc and 20 ml of ethanol . the mixture is stirred for 2 h at room temperature . the reaction mixture is poured into polystyrene petri dishes to evaporate . the resulting iridescent films are peeled off of the substrate to obtain free - standing composite films with a reflectance peak at ˜ 1445 nm . organosilica / ncc composite films from preparation 18 are placed in concentrated hcl and heated to 80 ° c . for 20 hours . the films were filtered , washed with water and placed in a solution of hydrogen peroxide ( 30 %, 20 ml ) and silver nitrate ( 0 . 015 g ) at 70 ° c . for 2 hours . the films were then filtered , placed in water and heated to 70 ° c . overnight . the films were filtered and allowed to air - dry . 145 mg of the iridescent films with a reflection peak at 1000 - 1100 nm are obtained . ir spectroscopy , tga , and elemental analysis confirmed that the cellulose is removed with retention of the ethylene and benzene bridges in the organosilica . n 2 adsorption measurements indicate that the product is mesoporous with a bet surface area of 684 m 2 / g and a specific pore volume of 1 . 07 cm 3 / g . 1 . davis , m . e . ordered porous materials for emerging applications . nature 417 , 813 - 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